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 $51.33   12.461%   $57.7262   $57.73   $57.75   $57.70  
  Purchase #2 $236.48   4.233%   $246.4902   $246.49   $246.50   $246.50  
  Purchase #3 $166.47   7.193%   $178.4442   $178.44   $178.45   $178.40  
  Purchase #4 $138.99   3.298%   $143.5739   $143.57   $143.55   $143.60  
  Purchase #5 $141.47   13.835%   $161.0424   $161.04   $161.05   $161.00  
  Purchase #6 $229.85   13.434%   $260.728   $260.73   $260.75   $260.70  
  Purchase #7 $207.44   5.770%   $219.4093   $219.41   $219.40   $219.40  
  7 purchase totals = $1,172.03       $1,267.4142   $1,267.41   $1,267.45   $1,267.30