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 $247.61   5.208%   $260.5055   $260.51   $260.50   $260.50  
  Purchase #2 $159.48   11.534%   $177.8744   $177.87   $177.85   $177.90  
  Purchase #3 $170.70   5.435%   $179.9775   $179.98   $180.00   $180.00  
  Purchase #4 $192.35   3.130%   $198.3706   $198.37   $198.35   $198.40  
  Purchase #5 $239.32   10.506%   $264.463   $264.46   $264.45   $264.50  
  Purchase #6 $136.92   5.326%   $144.2124   $144.21   $144.20   $144.20  
  Purchase #7 $127.40   4.769%   $133.4757   $133.48   $133.50   $133.50  
  7 purchase totals = $1,273.78       $1,358.8791   $1,358.88   $1,358.85   $1,359.00