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 $244.70   9.509%   $267.9685   $267.97   $267.95   $268.00  
  Purchase #2 $238.88   11.761%   $266.9747   $266.97   $266.95   $267.00  
  Purchase #3 $18.76   9.394%   $20.5223   $20.52   $20.50   $20.50  
  Purchase #4 $119.28   10.845%   $132.2159   $132.22   $132.20   $132.20  
  Purchase #5 $138.26   10.655%   $152.9916   $152.99   $153.00   $153.00  
  Purchase #6 $117.68   10.601%   $130.1553   $130.16   $130.15   $130.20  
  Purchase #7 $190.99   5.800%   $202.0674   $202.07   $202.05   $202.10  
  7 purchase totals = $1,068.55       $1,172.8957   $1,172.90   $1,172.80   $1,173.00