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 $67.48   12.374%   $75.83   $75.83   $75.85   $75.80  
  Purchase #2 $67.95   11.589%   $75.8247   $75.82   $75.80   $75.80  
  Purchase #3 $169.78   7.267%   $182.1179   $182.12   $182.10   $182.10  
  Purchase #4 $213.26   12.176%   $239.2265   $239.23   $239.25   $239.20  
  Purchase #5 $142.35   11.724%   $159.0391   $159.04   $159.05   $159.00  
  Purchase #6 $21.58   13.471%   $24.487   $24.49   $24.50   $24.50  
  Purchase #7 $80.85   7.699%   $87.0746   $87.07   $87.05   $87.10  
  7 purchase totals = $763.25       $843.5998   $843.60   $843.60   $843.50