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 $52.75   13.818%   $60.039   $60.04   $60.05   $60.00  
  Purchase #2 $12.28   11.348%   $13.6735   $13.67   $13.65   $13.70  
  Purchase #3 $81.30   4.286%   $84.7845   $84.78   $84.80   $84.80  
  Purchase #4 $97.65   11.334%   $108.7177   $108.72   $108.70   $108.70  
  Purchase #5 $201.77   11.369%   $224.7092   $224.71   $224.70   $224.70  
  Purchase #6 $232.74   12.125%   $260.9597   $260.96   $260.95   $261.00  
  Purchase #7 $155.69   9.372%   $170.2813   $170.28   $170.30   $170.30  
  7 purchase totals = $834.18       $923.1649   $923.16   $923.15   $923.20