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 $118.64   4.104%   $123.509   $123.51   $123.50   $123.50  
  Purchase #2 $44.33   6.208%   $47.082   $47.08   $47.10   $47.10  
  Purchase #3 $235.46   9.420%   $257.6403   $257.64   $257.65   $257.60  
  Purchase #4 $156.55   12.769%   $176.5399   $176.54   $176.55   $176.50  
  Purchase #5 $43.52   7.692%   $46.8676   $46.87   $46.85   $46.90  
  Purchase #6 $125.34   3.616%   $129.8723   $129.87   $129.85   $129.90  
  Purchase #7 $118.37   7.113%   $126.7897   $126.79   $126.80   $126.80  
  7 purchase totals = $842.21       $908.3008   $908.30   $908.30   $908.30