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 $88.53   4.721%   $92.7095   $92.71   $92.70   $92.70  
  Purchase #2 $194.48   10.874%   $215.6278   $215.63   $215.65   $215.60  
  Purchase #3 $238.44   3.672%   $247.1955   $247.20   $247.20   $247.20  
  Purchase #4 $235.59   6.259%   $250.3356   $250.34   $250.35   $250.30  
  Purchase #5 $215.71   3.783%   $223.8703   $223.87   $223.85   $223.90  
  Purchase #6 $234.31   3.320%   $242.0891   $242.09   $242.10   $242.10  
  Purchase #7 $78.29   6.575%   $83.4376   $83.44   $83.45   $83.40  
  7 purchase totals = $1,285.35       $1,355.2654   $1,355.28   $1,355.30   $1,355.20