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 $202.45   3.781%   $210.1046   $210.10   $210.10   $210.10  
  Purchase #2 $167.67   6.130%   $177.9482   $177.95   $177.95   $177.90  
  Purchase #3 $60.50   9.187%   $66.0581   $66.06   $66.05   $66.10  
  Purchase #4 $243.32   12.597%   $273.971   $273.97   $273.95   $274.00  
  Purchase #5 $77.31   11.622%   $86.295   $86.30   $86.30   $86.30  
  Purchase #6 $110.52   12.481%   $124.314   $124.31   $124.30   $124.30  
  Purchase #7 $40.88   6.535%   $43.5515   $43.55   $43.55   $43.60  
  7 purchase totals = $902.65       $982.2424   $982.24   $982.20   $982.30