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 $68.39   3.403%   $70.7173   $70.72   $70.70   $70.70  
  Purchase #2 $25.97   4.457%   $27.1275   $27.13   $27.15   $27.10  
  Purchase #3 $9.84   11.347%   $10.9565   $10.96   $10.95   $11.00  
  Purchase #4 $68.78   8.554%   $74.6634   $74.66   $74.65   $74.70  
  Purchase #5 $225.49   8.219%   $244.023   $244.02   $244.00   $244.00  
  Purchase #6 $212.96   12.414%   $239.3969   $239.40   $239.40   $239.40  
  Purchase #7 $213.57   6.440%   $227.3239   $227.32   $227.30   $227.30  
  7 purchase totals = $825.00       $894.2085   $894.21   $894.15   $894.20