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 $13.93   5.399%   $14.6821   $14.68   $14.70   $14.70  
  Purchase #2 $123.62   11.340%   $137.6385   $137.64   $137.65   $137.60  
  Purchase #3 $236.92   3.205%   $244.5133   $244.51   $244.50   $244.50  
  Purchase #4 $5.47   10.314%   $6.0342   $6.03   $6.05   $6.00  
  Purchase #5 $120.52   12.200%   $135.2234   $135.22   $135.20   $135.20  
  Purchase #6 $33.51   7.370%   $35.9797   $35.98   $36.00   $36.00  
  Purchase #7 $180.50   8.677%   $196.162   $196.16   $196.15   $196.20  
  7 purchase totals = $714.47       $770.2332   $770.22   $770.25   $770.20