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 $62.42   8.157%   $67.5116   $67.51   $67.50   $67.50  
  Purchase #2 $167.85   4.641%   $175.6399   $175.64   $175.65   $175.60  
  Purchase #3 $54.76   3.793%   $56.837   $56.84   $56.85   $56.80  
  Purchase #4 $178.94   12.321%   $200.9872   $200.99   $201.00   $201.00  
  Purchase #5 $72.45   5.284%   $76.2783   $76.28   $76.30   $76.30  
  Purchase #6 $17.59   13.474%   $19.9601   $19.96   $19.95   $20.00  
  Purchase #7 $169.43   4.582%   $177.1933   $177.19   $177.20   $177.20  
  7 purchase totals = $723.44       $774.4074   $774.41   $774.45   $774.40