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 $52.39   13.104%   $59.2552   $59.26   $59.25   $59.30  
  Purchase #2 $237.53   4.442%   $248.0811   $248.08   $248.10   $248.10  
  Purchase #3 $127.31   7.362%   $136.6826   $136.68   $136.70   $136.70  
  Purchase #4 $32.54   12.574%   $36.6316   $36.63   $36.65   $36.60  
  Purchase #5 $197.68   4.827%   $207.222   $207.22   $207.20   $207.20  
  Purchase #6 $125.28   9.603%   $137.3106   $137.31   $137.30   $137.30  
  Purchase #7 $47.55   6.371%   $50.5794   $50.58   $50.60   $50.60  
  7 purchase totals = $820.28       $875.7625   $875.76   $875.80   $875.80