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 $218.59   11.720%   $244.2087   $244.21   $244.20   $244.20  
  Purchase #2 $150.92   7.241%   $161.8481   $161.85   $161.85   $161.80  
  Purchase #3 $78.68   4.406%   $82.1466   $82.15   $82.15   $82.10  
  Purchase #4 $221.76   11.406%   $247.0539   $247.05   $247.05   $247.10  
  Purchase #5 $208.89   10.703%   $231.2475   $231.25   $231.25   $231.20  
  Purchase #6 $120.70   5.851%   $127.7622   $127.76   $127.75   $127.80  
  Purchase #7 $92.97   6.334%   $98.8587   $98.86   $98.85   $98.90  
  7 purchase totals = $1,092.51       $1,193.1257   $1,193.13   $1,193.10   $1,193.10