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 $65.66   5.853%   $69.5031   $69.50   $69.50   $69.50  
  Purchase #2 $32.43   11.264%   $36.0829   $36.08   $36.10   $36.10  
  Purchase #3 $249.73   5.461%   $263.3678   $263.37   $263.35   $263.40  
  Purchase #4 $148.91   9.289%   $162.7422   $162.74   $162.75   $162.70  
  Purchase #5 $22.53   9.798%   $24.7375   $24.74   $24.75   $24.70  
  Purchase #6 $165.44   9.350%   $180.9086   $180.91   $180.90   $180.90  
  Purchase #7 $31.31   11.705%   $34.9748   $34.97   $34.95   $35.00  
  7 purchase totals = $716.01       $772.3169   $772.31   $772.30   $772.30