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 $235.84   5.251%   $248.224   $248.22   $248.20   $248.20  
  Purchase #2 $89.28   4.458%   $93.2601   $93.26   $93.25   $93.30  
  Purchase #3 $75.75   12.421%   $85.1589   $85.16   $85.15   $85.20  
  Purchase #4 $69.55   7.714%   $74.9151   $74.92   $74.90   $74.90  
  Purchase #5 $44.87   8.380%   $48.6301   $48.63   $48.65   $48.60  
  Purchase #6 $226.41   8.541%   $245.7477   $245.75   $245.75   $245.70  
  Purchase #7 $154.82   7.230%   $166.0135   $166.01   $166.00   $166.00  
  7 purchase totals = $896.52       $961.9494   $961.95   $961.90   $961.90