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 $216.51   4.855%   $227.0216   $227.02   $227.00   $227.00  
  Purchase #2 $176.28   8.643%   $191.5159   $191.52   $191.50   $191.50  
  Purchase #3 $15.33   9.346%   $16.7627   $16.76   $16.75   $16.80  
  Purchase #4 $237.95   5.461%   $250.9444   $250.94   $250.95   $250.90  
  Purchase #5 $203.91   11.187%   $226.7214   $226.72   $226.70   $226.70  
  Purchase #6 $156.47   3.514%   $161.9684   $161.97   $161.95   $162.00  
  Purchase #7 $200.72   11.243%   $223.2869   $223.29   $223.30   $223.30  
  7 purchase totals = $1,207.17       $1,298.2213   $1,298.22   $1,298.15   $1,298.20