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 $240.39   3.131%   $247.9166   $247.92   $247.90   $247.90  
  Purchase #2 $227.87   6.431%   $242.5243   $242.52   $242.50   $242.50  
  Purchase #3 $110.89   6.772%   $118.3995   $118.40   $118.40   $118.40  
  Purchase #4 $64.70   13.728%   $73.582   $73.58   $73.60   $73.60  
  Purchase #5 $176.76   4.653%   $184.9846   $184.98   $185.00   $185.00  
  Purchase #6 $127.76   11.340%   $142.248   $142.25   $142.25   $142.20  
  Purchase #7 $233.87   4.755%   $244.9905   $244.99   $245.00   $245.00  
  7 purchase totals = $1,182.24       $1,254.6455   $1,254.64   $1,254.65   $1,254.60