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 $17.90   6.616%   $19.0843   $19.08   $19.10   $19.10  
  Purchase #2 $5.86   3.584%   $6.07   $6.07   $6.05   $6.10  
  Purchase #3 $72.80   3.634%   $75.4456   $75.45   $75.45   $75.40  
  Purchase #4 $20.69   5.759%   $21.8815   $21.88   $21.90   $21.90  
  Purchase #5 $175.44   11.188%   $195.0682   $195.07   $195.05   $195.10  
  Purchase #6 $109.50   10.614%   $121.1223   $121.12   $121.10   $121.10  
  Purchase #7 $108.98   10.830%   $120.7825   $120.78   $120.80   $120.80  
  7 purchase totals = $511.17       $559.4544   $559.45   $559.45   $559.50