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 $124.31   8.494%   $134.8689   $134.87   $134.85   $134.90  
  Purchase #2 $250.65   13.607%   $284.7559   $284.76   $284.75   $284.80  
  Purchase #3 $49.80   6.679%   $53.1261   $53.13   $53.15   $53.10  
  Purchase #4 $237.93   4.134%   $247.766   $247.77   $247.75   $247.80  
  Purchase #5 $88.54   4.720%   $92.7191   $92.72   $92.70   $92.70  
  Purchase #6 $180.28   13.611%   $204.8179   $204.82   $204.80   $204.80  
  Purchase #7 $62.42   3.507%   $64.6091   $64.61   $64.60   $64.60  
  7 purchase totals = $993.93       $1,082.6630   $1,082.68   $1,082.60   $1,082.70