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 $41.68   3.235%   $43.0283   $43.03   $43.05   $43.00  
  Purchase #2 $60.84   3.358%   $62.883   $62.88   $62.90   $62.90  
  Purchase #3 $52.51   9.535%   $57.5168   $57.52   $57.50   $57.50  
  Purchase #4 $123.82   5.163%   $130.2128   $130.21   $130.20   $130.20  
  Purchase #5 $45.27   8.455%   $49.0976   $49.10   $49.10   $49.10  
  Purchase #6 $236.98   8.418%   $256.929   $256.93   $256.95   $256.90  
  Purchase #7 $158.51   9.472%   $173.5241   $173.52   $173.50   $173.50  
  7 purchase totals = $719.61       $773.1916   $773.19   $773.20   $773.10