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 $220.86   4.638%   $231.1035   $231.10   $231.10   $231.10  
  Purchase #2 $141.47   3.178%   $145.9659   $145.97   $145.95   $146.00  
  Purchase #3 $200.90   3.463%   $207.8572   $207.86   $207.85   $207.90  
  Purchase #4 $75.34   9.784%   $82.7113   $82.71   $82.70   $82.70  
  Purchase #5 $124.37   9.718%   $136.4563   $136.46   $136.45   $136.50  
  Purchase #6 $60.93   11.187%   $67.7462   $67.75   $67.75   $67.70  
  Purchase #7 $16.41   8.406%   $17.7894   $17.79   $17.80   $17.80  
  7 purchase totals = $840.28       $889.6298   $889.64   $889.60   $889.70