Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.96   7.387%   $265.2029   $265.20   $265.20   $265.20  
  Purchase #2 $100.55   9.458%   $110.06   $110.06   $110.05   $110.10  
  Purchase #3 $140.30   12.641%   $158.0353   $158.04   $158.05   $158.00  
  Purchase #4 $160.80   11.296%   $178.964   $178.96   $178.95   $179.00  
  Purchase #5 $210.64   9.323%   $230.278   $230.28   $230.30   $230.30  
  Purchase #6 $126.39   11.776%   $141.2737   $141.27   $141.25   $141.30  
  Purchase #7 $151.42   13.564%   $171.9586   $171.96   $171.95   $172.00  
  7 purchase totals = $1,137.06       $1,255.7725   $1,255.77   $1,255.75   $1,255.90