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 $102.53   9.425%   $112.1935   $112.19   $112.20   $112.20  
  Purchase #2 $160.95   7.359%   $172.7943   $172.79   $172.80   $172.80  
  Purchase #3 $205.93   4.851%   $215.9197   $215.92   $215.90   $215.90  
  Purchase #4 $54.28   7.562%   $58.3847   $58.38   $58.40   $58.40  
  Purchase #5 $62.77   5.564%   $66.2625   $66.26   $66.25   $66.30  
  Purchase #6 $155.75   5.193%   $163.8381   $163.84   $163.85   $163.80  
  Purchase #7 $219.43   10.779%   $243.0824   $243.08   $243.10   $243.10  
  7 purchase totals = $961.64       $1,032.4752   $1,032.46   $1,032.50   $1,032.50