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 $58.29   7.226%   $62.502   $62.50   $62.50   $62.50  
  Purchase #2 $46.78   7.217%   $50.1561   $50.16   $50.15   $50.20  
  Purchase #3 $31.42   8.707%   $34.1557   $34.16   $34.15   $34.20  
  Purchase #4 $40.41   10.672%   $44.7226   $44.72   $44.70   $44.70  
  Purchase #5 $189.90   9.496%   $207.9329   $207.93   $207.95   $207.90  
  Purchase #6 $207.32   13.608%   $235.5321   $235.53   $235.55   $235.50  
  Purchase #7 $150.72   11.689%   $168.3377   $168.34   $168.35   $168.30  
  7 purchase totals = $724.84       $803.3391   $803.34   $803.35   $803.30