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 $245.29   6.284%   $260.704   $260.70   $260.70   $260.70  
  Purchase #2 $28.66   3.535%   $29.6731   $29.67   $29.65   $29.70  
  Purchase #3 $74.78   7.634%   $80.4887   $80.49   $80.50   $80.50  
  Purchase #4 $19.47   12.337%   $21.872   $21.87   $21.85   $21.90  
  Purchase #5 $55.57   8.645%   $60.374   $60.37   $60.35   $60.40  
  Purchase #6 $84.88   6.461%   $90.3641   $90.36   $90.35   $90.40  
  Purchase #7 $201.80   3.777%   $209.422   $209.42   $209.40   $209.40  
  7 purchase totals = $710.45       $752.8979   $752.88   $752.80   $753.00