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 $230.97   11.160%   $256.7463   $256.75   $256.75   $256.70  
  Purchase #2 $131.56   4.340%   $137.2697   $137.27   $137.25   $137.30  
  Purchase #3 $103.43   9.535%   $113.2921   $113.29   $113.30   $113.30  
  Purchase #4 $235.59   13.462%   $267.3051   $267.31   $267.30   $267.30  
  Purchase #5 $191.78   9.697%   $210.3769   $210.38   $210.40   $210.40  
  Purchase #6 $29.93   13.476%   $33.9634   $33.96   $33.95   $34.00  
  Purchase #7 $194.36   8.261%   $210.4161   $210.42   $210.40   $210.40  
  7 purchase totals = $1,117.62       $1,229.3696   $1,229.38   $1,229.35   $1,229.40