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 $94.68   9.761%   $103.9217   $103.92   $103.90   $103.90  
  Purchase #2 $185.39   8.867%   $201.8285   $201.83   $201.85   $201.80  
  Purchase #3 $76.69   10.144%   $84.4694   $84.47   $84.45   $84.50  
  Purchase #4 $203.30   9.142%   $221.8857   $221.89   $221.90   $221.90  
  Purchase #5 $99.29   8.232%   $107.4636   $107.46   $107.45   $107.50  
  Purchase #6 $214.71   11.769%   $239.9792   $239.98   $240.00   $240.00  
  Purchase #7 $23.65   13.634%   $26.8744   $26.87   $26.85   $26.90  
  7 purchase totals = $897.71       $986.4225   $986.42   $986.40   $986.50