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 $64.82   3.381%   $67.0116   $67.01   $67.00   $67.00  
  Purchase #2 $77.65   12.731%   $87.5356   $87.54   $87.55   $87.50  
  Purchase #3 $70.38   6.509%   $74.961   $74.96   $74.95   $75.00  
  Purchase #4 $63.53   7.609%   $68.364   $68.36   $68.35   $68.40  
  Purchase #5 $58.37   4.701%   $61.114   $61.11   $61.10   $61.10  
  Purchase #6 $187.60   11.147%   $208.5118   $208.51   $208.50   $208.50  
  Purchase #7 $116.27   11.386%   $129.5085   $129.51   $129.50   $129.50  
  7 purchase totals = $638.62       $697.0065   $697.00   $696.95   $697.00