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 $58.27   8.354%   $63.1379   $63.14   $63.15   $63.10  
  Purchase #2 $145.82   8.222%   $157.8093   $157.81   $157.80   $157.80  
  Purchase #3 $84.26   9.159%   $91.9774   $91.98   $92.00   $92.00  
  Purchase #4 $66.43   6.759%   $70.92   $70.92   $70.90   $70.90  
  Purchase #5 $62.76   6.145%   $66.6166   $66.62   $66.60   $66.60  
  Purchase #6 $108.49   9.338%   $118.6208   $118.62   $118.60   $118.60  
  Purchase #7 $126.29   4.500%   $131.9731   $131.97   $131.95   $132.00  
  7 purchase totals = $652.32       $701.0551   $701.06   $701.00   $701.00