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 $49.66   6.685%   $52.9798   $52.98   $53.00   $53.00  
  Purchase #2 $184.93   5.111%   $194.3818   $194.38   $194.40   $194.40  
  Purchase #3 $177.49   4.418%   $185.3315   $185.33   $185.35   $185.30  
  Purchase #4 $229.39   8.245%   $248.3032   $248.30   $248.30   $248.30  
  Purchase #5 $36.60   12.330%   $41.1128   $41.11   $41.10   $41.10  
  Purchase #6 $67.97   7.801%   $73.2723   $73.27   $73.25   $73.30  
  Purchase #7 $75.40   8.476%   $81.7909   $81.79   $81.80   $81.80  
  7 purchase totals = $821.44       $877.1723   $877.16   $877.20   $877.20