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 $134.99   10.602%   $149.3016   $149.30   $149.30   $149.30  
  Purchase #2 $227.63   9.862%   $250.0789   $250.08   $250.10   $250.10  
  Purchase #3 $99.25   4.407%   $103.6239   $103.62   $103.60   $103.60  
  Purchase #4 $154.98   8.399%   $167.9968   $168.00   $168.00   $168.00  
  Purchase #5 $137.82   13.215%   $156.0329   $156.03   $156.05   $156.00  
  Purchase #6 $109.25   5.543%   $115.3057   $115.31   $115.30   $115.30  
  Purchase #7 $30.40   10.745%   $33.6665   $33.67   $33.65   $33.70  
  7 purchase totals = $894.32       $976.0063   $976.01   $976.00   $976.00