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 $250.27   10.282%   $276.0028   $276.00   $276.00   $276.00  
  Purchase #2 $48.39   12.261%   $54.3231   $54.32   $54.30   $54.30  
  Purchase #3 $187.32   11.781%   $209.3882   $209.39   $209.40   $209.40  
  Purchase #4 $236.25   4.584%   $247.0797   $247.08   $247.10   $247.10  
  Purchase #5 $173.90   12.303%   $195.2949   $195.29   $195.30   $195.30  
  Purchase #6 $5.94   4.664%   $6.217   $6.22   $6.20   $6.20  
  Purchase #7 $173.81   6.775%   $185.5856   $185.59   $185.60   $185.60  
  7 purchase totals = $1,075.88       $1,173.8913   $1,173.89   $1,173.90   $1,173.90