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 $67.77   6.380%   $72.0937   $72.09   $72.10   $72.10  
  Purchase #2 $125.81   8.592%   $136.6196   $136.62   $136.60   $136.60  
  Purchase #3 $143.45   7.587%   $154.3336   $154.33   $154.35   $154.30  
  Purchase #4 $172.46   5.197%   $181.4227   $181.42   $181.40   $181.40  
  Purchase #5 $111.42   6.480%   $118.64   $118.64   $118.65   $118.60  
  Purchase #6 $234.62   6.531%   $249.943   $249.94   $249.95   $249.90  
  Purchase #7 $60.41   12.645%   $68.0488   $68.05   $68.05   $68.00  
  7 purchase totals = $915.94       $981.1014   $981.09   $981.10   $980.90