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 $226.81   4.138%   $236.1954   $236.20   $236.20   $236.20  
  Purchase #2 $103.25   13.255%   $116.9358   $116.94   $116.95   $116.90  
  Purchase #3 $9.66   12.235%   $10.8419   $10.84   $10.85   $10.80  
  Purchase #4 $140.56   3.615%   $145.6412   $145.64   $145.65   $145.60  
  Purchase #5 $158.34   5.391%   $166.8761   $166.88   $166.90   $166.90  
  Purchase #6 $221.50   3.612%   $229.5006   $229.50   $229.50   $229.50  
  Purchase #7 $244.50   6.667%   $260.8008   $260.80   $260.80   $260.80  
  7 purchase totals = $1,104.62       $1,166.7918   $1,166.80   $1,166.85   $1,166.70