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 $247.75   5.222%   $260.6875   $260.69   $260.70   $260.70  
  Purchase #2 $168.62   6.408%   $179.4252   $179.43   $179.45   $179.40  
  Purchase #3 $193.84   9.501%   $212.2567   $212.26   $212.25   $212.30  
  Purchase #4 $55.84   10.728%   $61.8305   $61.83   $61.85   $61.80  
  Purchase #5 $182.49   13.542%   $207.2028   $207.20   $207.20   $207.20  
  Purchase #6 $121.89   13.141%   $137.9076   $137.91   $137.90   $137.90  
  Purchase #7 $67.35   8.635%   $73.1657   $73.17   $73.15   $73.20  
  7 purchase totals = $1,037.78       $1,132.4760   $1,132.49   $1,132.50   $1,132.50