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 $29.60   8.197%   $32.0263   $32.03   $32.05   $32.00  
  Purchase #2 $147.37   8.268%   $159.5546   $159.55   $159.55   $159.60  
  Purchase #3 $193.61   3.574%   $200.5296   $200.53   $200.55   $200.50  
  Purchase #4 $59.72   5.721%   $63.1366   $63.14   $63.15   $63.10  
  Purchase #5 $93.43   4.148%   $97.3055   $97.31   $97.30   $97.30  
  Purchase #6 $132.37   7.303%   $142.037   $142.04   $142.05   $142.00  
  Purchase #7 $115.68   11.766%   $129.2909   $129.29   $129.30   $129.30  
  7 purchase totals = $771.78       $823.8805   $823.89   $823.95   $823.80