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 $45.41   6.449%   $48.3385   $48.34   $48.35   $48.30  
  Purchase #2 $63.46   6.728%   $67.7296   $67.73   $67.75   $67.70  
  Purchase #3 $69.68   5.631%   $73.6037   $73.60   $73.60   $73.60  
  Purchase #4 $162.60   8.606%   $176.5934   $176.59   $176.60   $176.60  
  Purchase #5 $31.38   7.612%   $33.7686   $33.77   $33.75   $33.80  
  Purchase #6 $188.56   10.796%   $208.9169   $208.92   $208.90   $208.90  
  Purchase #7 $85.36   11.297%   $95.0031   $95.00   $95.00   $95.00  
  7 purchase totals = $646.45       $703.9538   $703.95   $703.95   $703.90