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 $59.35   12.429%   $66.7266   $66.73   $66.75   $66.70  
  Purchase #2 $68.51   9.695%   $75.152   $75.15   $75.15   $75.20  
  Purchase #3 $128.62   6.550%   $137.0446   $137.04   $137.05   $137.00  
  Purchase #4 $41.88   5.577%   $44.2156   $44.22   $44.20   $44.20  
  Purchase #5 $53.44   6.706%   $57.0237   $57.02   $57.00   $57.00  
  Purchase #6 $165.36   11.344%   $184.1184   $184.12   $184.10   $184.10  
  Purchase #7 $208.70   13.474%   $236.8202   $236.82   $236.80   $236.80  
  7 purchase totals = $725.86       $801.1011   $801.10   $801.05   $801.00