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 $53.47   13.576%   $60.7291   $60.73   $60.75   $60.70  
  Purchase #2 $51.90   13.671%   $58.9952   $59.00   $59.00   $59.00  
  Purchase #3 $55.26   3.866%   $57.3964   $57.40   $57.40   $57.40  
  Purchase #4 $164.86   12.641%   $185.7   $185.70   $185.70   $185.70  
  Purchase #5 $213.86   4.505%   $223.4944   $223.49   $223.50   $223.50  
  Purchase #6 $184.94   8.244%   $200.1865   $200.19   $200.20   $200.20  
  Purchase #7 $76.57   10.513%   $84.6198   $84.62   $84.60   $84.60  
  7 purchase totals = $800.86       $871.1214   $871.13   $871.15   $871.10