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 $53.60   11.452%   $59.7383   $59.74   $59.75   $59.70  
  Purchase #2 $130.41   7.219%   $139.8243   $139.82   $139.80   $139.80  
  Purchase #3 $212.32   6.539%   $226.2036   $226.20   $226.20   $226.20  
  Purchase #4 $84.38   11.823%   $94.3562   $94.36   $94.35   $94.40  
  Purchase #5 $30.65   6.826%   $32.7422   $32.74   $32.75   $32.70  
  Purchase #6 $8.32   8.863%   $9.0574   $9.06   $9.05   $9.10  
  Purchase #7 $173.33   10.727%   $191.9231   $191.92   $191.90   $191.90  
  7 purchase totals = $693.01       $753.8451   $753.84   $753.80   $753.80