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 $169.39   4.310%   $176.6907   $176.69   $176.70   $176.70  
  Purchase #2 $157.61   11.614%   $175.9148   $175.91   $175.90   $175.90  
  Purchase #3 $121.39   3.696%   $125.8766   $125.88   $125.90   $125.90  
  Purchase #4 $70.73   3.597%   $73.2742   $73.27   $73.25   $73.30  
  Purchase #5 $94.86   3.284%   $97.9752   $97.98   $98.00   $98.00  
  Purchase #6 $129.94   11.706%   $145.1508   $145.15   $145.15   $145.20  
  Purchase #7 $75.75   12.503%   $85.221   $85.22   $85.20   $85.20  
  7 purchase totals = $819.67       $880.1033   $880.10   $880.10   $880.20