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 $183.26   5.457%   $193.2605   $193.26   $193.25   $193.30  
  Purchase #2 $147.88   9.142%   $161.3992   $161.40   $161.40   $161.40  
  Purchase #3 $173.36   9.578%   $189.9644   $189.96   $189.95   $190.00  
  Purchase #4 $119.87   5.271%   $126.1883   $126.19   $126.20   $126.20  
  Purchase #5 $68.32   6.270%   $72.6037   $72.60   $72.60   $72.60  
  Purchase #6 $37.71   13.814%   $42.9193   $42.92   $42.90   $42.90  
  Purchase #7 $197.27   4.635%   $206.4135   $206.41   $206.40   $206.40  
  7 purchase totals = $927.67       $992.7489   $992.74   $992.70   $992.80