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 $32.48   9.464%   $35.5539   $35.55   $35.55   $35.60  
  Purchase #2 $44.94   12.807%   $50.6955   $50.70   $50.70   $50.70  
  Purchase #3 $218.84   8.324%   $237.0562   $237.06   $237.05   $237.10  
  Purchase #4 $53.30   7.847%   $57.4825   $57.48   $57.50   $57.50  
  Purchase #5 $224.78   9.475%   $246.0779   $246.08   $246.10   $246.10  
  Purchase #6 $244.67   8.299%   $264.9752   $264.98   $265.00   $265.00  
  Purchase #7 $89.66   12.639%   $100.9921   $100.99   $101.00   $101.00  
  7 purchase totals = $908.67       $992.8333   $992.84   $992.90   $993.00