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 $60.85   7.181%   $65.2196   $65.22   $65.20   $65.20  
  Purchase #2 $96.78   11.454%   $107.8652   $107.87   $107.85   $107.90  
  Purchase #3 $204.39   7.149%   $219.0018   $219.00   $219.00   $219.00  
  Purchase #4 $197.55   11.673%   $220.61   $220.61   $220.60   $220.60  
  Purchase #5 $90.64   9.354%   $99.1185   $99.12   $99.10   $99.10  
  Purchase #6 $69.38   3.114%   $71.5405   $71.54   $71.55   $71.50  
  Purchase #7 $236.73   13.154%   $267.8695   $267.87   $267.85   $267.90  
  7 purchase totals = $956.32       $1,051.2251   $1,051.23   $1,051.15   $1,051.20