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 $61.45   3.647%   $63.6911   $63.69   $63.70   $63.70  
  Purchase #2 $167.61   13.302%   $189.9055   $189.91   $189.90   $189.90  
  Purchase #3 $67.53   8.540%   $73.2971   $73.30   $73.30   $73.30  
  Purchase #4 $91.74   8.341%   $99.392   $99.39   $99.40   $99.40  
  Purchase #5 $62.33   11.300%   $69.3733   $69.37   $69.35   $69.40  
  Purchase #6 $185.69   4.479%   $194.0071   $194.01   $194.00   $194.00  
  Purchase #7 $74.73   11.529%   $83.3456   $83.35   $83.35   $83.30  
  7 purchase totals = $711.08       $773.0117   $773.02   $773.00   $773.00