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 $112.53   9.567%   $123.2957   $123.30   $123.30   $123.30  
  Purchase #2 $176.94   11.430%   $197.1642   $197.16   $197.15   $197.20  
  Purchase #3 $83.63   10.473%   $92.3886   $92.39   $92.40   $92.40  
  Purchase #4 $76.88   11.224%   $85.509   $85.51   $85.50   $85.50  
  Purchase #5 $128.79   6.130%   $136.6848   $136.68   $136.70   $136.70  
  Purchase #6 $133.70   8.188%   $144.6474   $144.65   $144.65   $144.60  
  Purchase #7 $241.77   10.476%   $267.0978   $267.10   $267.10   $267.10  
  7 purchase totals = $954.24       $1,046.7875   $1,046.79   $1,046.80   $1,046.80