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 $207.61   8.359%   $224.9641   $224.96   $224.95   $225.00  
  Purchase #2 $132.32   4.787%   $138.6542   $138.65   $138.65   $138.70  
  Purchase #3 $178.76   8.757%   $194.414   $194.41   $194.40   $194.40  
  Purchase #4 $203.80   4.643%   $213.2624   $213.26   $213.25   $213.30  
  Purchase #5 $42.71   13.845%   $48.6232   $48.62   $48.60   $48.60  
  Purchase #6 $236.99   3.503%   $245.2918   $245.29   $245.30   $245.30  
  Purchase #7 $171.38   3.755%   $177.8153   $177.82   $177.80   $177.80  
  7 purchase totals = $1,173.57       $1,243.0250   $1,243.01   $1,242.95   $1,243.10