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 $131.38   4.151%   $136.8336   $136.83   $136.85   $136.80  
  Purchase #2 $191.84   5.234%   $201.8809   $201.88   $201.90   $201.90  
  Purchase #3 $189.63   8.494%   $205.7372   $205.74   $205.75   $205.70  
  Purchase #4 $123.99   11.794%   $138.6134   $138.61   $138.60   $138.60  
  Purchase #5 $122.86   11.737%   $137.2801   $137.28   $137.30   $137.30  
  Purchase #6 $195.92   3.677%   $203.124   $203.12   $203.10   $203.10  
  Purchase #7 $203.71   9.613%   $223.2926   $223.29   $223.30   $223.30  
  7 purchase totals = $1,159.33       $1,246.7618   $1,246.75   $1,246.80   $1,246.70