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 $38.54   11.533%   $42.9848   $42.98   $43.00   $43.00  
  Purchase #2 $64.41   3.501%   $66.665   $66.67   $66.65   $66.70  
  Purchase #3 $229.88   7.853%   $247.9325   $247.93   $247.95   $247.90  
  Purchase #4 $56.86   12.839%   $64.1603   $64.16   $64.15   $64.20  
  Purchase #5 $178.94   11.393%   $199.3266   $199.33   $199.35   $199.30  
  Purchase #6 $52.78   7.707%   $56.8478   $56.85   $56.85   $56.80  
  Purchase #7 $210.96   3.819%   $219.0166   $219.02   $219.00   $219.00  
  7 purchase totals = $832.37       $896.9336   $896.94   $896.95   $896.90