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 $232.72   11.594%   $259.7016   $259.70   $259.70   $259.70  
  Purchase #2 $195.94   10.217%   $215.9592   $215.96   $215.95   $216.00  
  Purchase #3 $122.86   4.474%   $128.3568   $128.36   $128.35   $128.40  
  Purchase #4 $220.45   6.611%   $235.0239   $235.02   $235.00   $235.00  
  Purchase #5 $241.43   3.527%   $249.9452   $249.95   $249.95   $249.90  
  Purchase #6 $47.71   5.466%   $50.3178   $50.32   $50.30   $50.30  
  Purchase #7 $18.47   11.559%   $20.6049   $20.60   $20.60   $20.60  
  7 purchase totals = $1,079.58       $1,159.9094   $1,159.91   $1,159.85   $1,159.90