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 $7.58   10.485%   $8.3748   $8.37   $8.35   $8.40  
  Purchase #2 $173.72   3.704%   $180.1546   $180.15   $180.15   $180.20  
  Purchase #3 $203.91   6.710%   $217.5924   $217.59   $217.60   $217.60  
  Purchase #4 $222.38   3.453%   $230.0588   $230.06   $230.05   $230.10  
  Purchase #5 $203.51   7.187%   $218.1363   $218.14   $218.15   $218.10  
  Purchase #6 $196.43   3.813%   $203.9199   $203.92   $203.90   $203.90  
  Purchase #7 $158.87   5.131%   $167.0216   $167.02   $167.00   $167.00  
  7 purchase totals = $1,166.40       $1,225.2584   $1,225.25   $1,225.20   $1,225.30