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 $117.65   5.424%   $124.0313   $124.03   $124.05   $124.00  
  Purchase #2 $70.48   5.874%   $74.62   $74.62   $74.60   $74.60  
  Purchase #3 $143.43   11.252%   $159.5687   $159.57   $159.55   $159.60  
  Purchase #4 $235.67   9.392%   $257.8041   $257.80   $257.80   $257.80  
  Purchase #5 $139.99   7.844%   $150.9708   $150.97   $150.95   $151.00  
  Purchase #6 $154.90   4.734%   $162.233   $162.23   $162.25   $162.20  
  Purchase #7 $48.52   6.714%   $51.7776   $51.78   $51.80   $51.80  
  7 purchase totals = $910.64       $981.0055   $981.00   $981.00   $981.00