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 $91.91   10.727%   $101.7692   $101.77   $101.75   $101.80  
  Purchase #2 $83.93   13.174%   $94.9869   $94.99   $95.00   $95.00  
  Purchase #3 $59.94   10.199%   $66.0533   $66.05   $66.05   $66.10  
  Purchase #4 $110.91   4.832%   $116.2692   $116.27   $116.25   $116.30  
  Purchase #5 $177.63   8.613%   $192.9293   $192.93   $192.95   $192.90  
  Purchase #6 $120.67   4.594%   $126.2136   $126.21   $126.20   $126.20  
  Purchase #7 $149.51   3.379%   $154.5619   $154.56   $154.55   $154.60  
  7 purchase totals = $794.50       $852.7834   $852.78   $852.75   $852.90