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 $63.71   6.513%   $67.8594   $67.86   $67.85   $67.90  
  Purchase #2 $93.47   4.475%   $97.6528   $97.65   $97.65   $97.70  
  Purchase #3 $58.60   9.614%   $64.2338   $64.23   $64.25   $64.20  
  Purchase #4 $241.62   9.114%   $263.6412   $263.64   $263.65   $263.60  
  Purchase #5 $16.72   9.293%   $18.2738   $18.27   $18.25   $18.30  
  Purchase #6 $94.70   7.720%   $102.0108   $102.01   $102.00   $102.00  
  Purchase #7 $54.52   5.664%   $57.608   $57.61   $57.60   $57.60  
  7 purchase totals = $623.34       $671.2798   $671.27   $671.25   $671.30