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 $87.63   11.793%   $97.9642   $97.96   $97.95   $98.00  
  Purchase #2 $60.81   10.106%   $66.9555   $66.96   $66.95   $67.00  
  Purchase #3 $72.99   3.570%   $75.5957   $75.60   $75.60   $75.60  
  Purchase #4 $56.61   5.634%   $59.7994   $59.80   $59.80   $59.80  
  Purchase #5 $187.58   11.384%   $208.9341   $208.93   $208.95   $208.90  
  Purchase #6 $32.46   10.452%   $35.8527   $35.85   $35.85   $35.90  
  Purchase #7 $22.31   5.407%   $23.5163   $23.52   $23.50   $23.50  
  7 purchase totals = $520.39       $568.6179   $568.62   $568.60   $568.70