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 $60.47   11.210%   $67.2487   $67.25   $67.25   $67.20  
  Purchase #2 $133.33   4.210%   $138.9432   $138.94   $138.95   $138.90  
  Purchase #3 $21.64   9.206%   $23.6322   $23.63   $23.65   $23.60  
  Purchase #4 $183.97   11.460%   $205.053   $205.05   $205.05   $205.10  
  Purchase #5 $182.97   6.553%   $194.96   $194.96   $194.95   $195.00  
  Purchase #6 $156.99   9.769%   $172.3264   $172.33   $172.35   $172.30  
  Purchase #7 $159.73   13.413%   $181.1546   $181.15   $181.15   $181.20  
  7 purchase totals = $899.10       $983.3181   $983.31   $983.35   $983.30