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 $53.85   11.849%   $60.2307   $60.23   $60.25   $60.20  
  Purchase #2 $208.54   8.870%   $227.0375   $227.04   $227.05   $227.00  
  Purchase #3 $43.41   11.767%   $48.5181   $48.52   $48.50   $48.50  
  Purchase #4 $219.38   12.182%   $246.1049   $246.10   $246.10   $246.10  
  Purchase #5 $54.84   7.735%   $59.0819   $59.08   $59.10   $59.10  
  Purchase #6 $61.81   11.407%   $68.8607   $68.86   $68.85   $68.90  
  Purchase #7 $118.81   3.229%   $122.6464   $122.65   $122.65   $122.60  
  7 purchase totals = $760.64       $832.4802   $832.48   $832.50   $832.40