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 $57.60   6.598%   $61.4004   $61.40   $61.40   $61.40  
  Purchase #2 $68.84   11.430%   $76.7084   $76.71   $76.70   $76.70  
  Purchase #3 $8.34   12.581%   $9.3893   $9.39   $9.40   $9.40  
  Purchase #4 $224.37   7.535%   $241.2763   $241.28   $241.30   $241.30  
  Purchase #5 $187.45   6.286%   $199.2331   $199.23   $199.25   $199.20  
  Purchase #6 $166.76   5.333%   $175.6533   $175.65   $175.65   $175.70  
  Purchase #7 $174.32   9.588%   $191.0338   $191.03   $191.05   $191.00  
  7 purchase totals = $887.68       $954.6946   $954.69   $954.75   $954.70