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 $61.40   11.619%   $68.5341   $68.53   $68.55   $68.50  
  Purchase #2 $129.94   12.644%   $146.3696   $146.37   $146.35   $146.40  
  Purchase #3 $121.29   6.427%   $129.0853   $129.09   $129.10   $129.10  
  Purchase #4 $197.52   5.502%   $208.3876   $208.39   $208.40   $208.40  
  Purchase #5 $168.69   9.427%   $184.5924   $184.59   $184.60   $184.60  
  Purchase #6 $162.91   6.434%   $173.3916   $173.39   $173.40   $173.40  
  Purchase #7 $207.50   12.729%   $233.9127   $233.91   $233.90   $233.90  
  7 purchase totals = $1,049.25       $1,144.2733   $1,144.27   $1,144.30   $1,144.30