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 $82.41   12.556%   $92.7574   $92.76   $92.75   $92.80  
  Purchase #2 $203.82   6.669%   $217.4128   $217.41   $217.40   $217.40  
  Purchase #3 $57.63   9.568%   $63.144   $63.14   $63.15   $63.10  
  Purchase #4 $224.55   10.150%   $247.3418   $247.34   $247.35   $247.30  
  Purchase #5 $44.73   11.590%   $49.9142   $49.91   $49.90   $49.90  
  Purchase #6 $168.94   4.366%   $176.3159   $176.32   $176.30   $176.30  
  Purchase #7 $154.45   12.693%   $174.0543   $174.05   $174.05   $174.10  
  7 purchase totals = $936.53       $1,020.9404   $1,020.93   $1,020.90   $1,020.90