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 $204.91   12.819%   $231.1774   $231.18   $231.20   $231.20  
  Purchase #2 $132.36   5.119%   $139.1355   $139.14   $139.15   $139.10  
  Purchase #3 $250.71   6.578%   $267.2017   $267.20   $267.20   $267.20  
  Purchase #4 $43.88   5.549%   $46.3149   $46.31   $46.30   $46.30  
  Purchase #5 $136.90   9.862%   $150.4011   $150.40   $150.40   $150.40  
  Purchase #6 $132.55   13.464%   $150.3965   $150.40   $150.40   $150.40  
  Purchase #7 $217.73   4.199%   $226.8725   $226.87   $226.85   $226.90  
  7 purchase totals = $1,119.04       $1,211.4996   $1,211.50   $1,211.50   $1,211.50