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 $246.51   6.827%   $263.3392   $263.34   $263.35   $263.30  
  Purchase #2 $26.39   12.652%   $29.7289   $29.73   $29.75   $29.70  
  Purchase #3 $38.91   4.427%   $40.6325   $40.63   $40.65   $40.60  
  Purchase #4 $116.98   9.294%   $127.8521   $127.85   $127.85   $127.90  
  Purchase #5 $127.46   4.757%   $133.5233   $133.52   $133.50   $133.50  
  Purchase #6 $185.94   4.328%   $193.9875   $193.99   $194.00   $194.00  
  Purchase #7 $84.75   12.297%   $95.1717   $95.17   $95.15   $95.20  
  7 purchase totals = $826.94       $884.2352   $884.23   $884.25   $884.20