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 $119.76   13.313%   $135.7036   $135.70   $135.70   $135.70  
  Purchase #2 $53.32   4.690%   $55.8207   $55.82   $55.80   $55.80  
  Purchase #3 $233.96   4.467%   $244.411   $244.41   $244.40   $244.40  
  Purchase #4 $98.86   3.800%   $102.6167   $102.62   $102.60   $102.60  
  Purchase #5 $84.94   10.465%   $93.829   $93.83   $93.85   $93.80  
  Purchase #6 $238.79   8.128%   $258.1989   $258.20   $258.20   $258.20  
  Purchase #7 $121.26   4.609%   $126.8489   $126.85   $126.85   $126.80  
  7 purchase totals = $950.89       $1,017.4288   $1,017.43   $1,017.40   $1,017.30