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 $241.96   8.112%   $261.5878   $261.59   $261.60   $261.60  
  Purchase #2 $61.81   9.366%   $67.5991   $67.60   $67.60   $67.60  
  Purchase #3 $223.46   10.421%   $246.7468   $246.75   $246.75   $246.70  
  Purchase #4 $78.39   11.413%   $87.3367   $87.34   $87.35   $87.30  
  Purchase #5 $243.61   5.216%   $256.3167   $256.32   $256.30   $256.30  
  Purchase #6 $231.75   10.547%   $256.1927   $256.19   $256.20   $256.20  
  Purchase #7 $167.70   4.863%   $175.8553   $175.86   $175.85   $175.90  
  7 purchase totals = $1,248.68       $1,351.6351   $1,351.65   $1,351.65   $1,351.60