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 $68.76   11.451%   $76.6337   $76.63   $76.65   $76.60  
  Purchase #2 $63.35   11.518%   $70.6467   $70.65   $70.65   $70.60  
  Purchase #3 $53.30   7.399%   $57.2437   $57.24   $57.25   $57.20  
  Purchase #4 $214.84   3.467%   $222.2885   $222.29   $222.30   $222.30  
  Purchase #5 $151.29   9.707%   $165.9757   $165.98   $166.00   $166.00  
  Purchase #6 $115.62   4.694%   $121.0472   $121.05   $121.05   $121.00  
  Purchase #7 $59.95   11.616%   $66.9138   $66.91   $66.90   $66.90  
  7 purchase totals = $727.11       $780.7493   $780.75   $780.80   $780.60