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 $241.75   13.830%   $275.184   $275.18   $275.20   $275.20  
  Purchase #2 $62.32   11.786%   $69.665   $69.67   $69.65   $69.70  
  Purchase #3 $177.50   11.168%   $197.3232   $197.32   $197.30   $197.30  
  Purchase #4 $67.70   10.868%   $75.0576   $75.06   $75.05   $75.10  
  Purchase #5 $62.97   6.594%   $67.1222   $67.12   $67.10   $67.10  
  Purchase #6 $105.94   13.225%   $119.9506   $119.95   $119.95   $120.00  
  Purchase #7 $231.32   11.138%   $257.0844   $257.08   $257.10   $257.10  
  7 purchase totals = $949.50       $1,061.3870   $1,061.38   $1,061.35   $1,061.50