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 $244.79   8.158%   $264.76   $264.76   $264.75   $264.80  
  Purchase #2 $61.71   4.135%   $64.2617   $64.26   $64.25   $64.30  
  Purchase #3 $9.88   8.477%   $10.7175   $10.72   $10.70   $10.70  
  Purchase #4 $183.90   5.855%   $194.6673   $194.67   $194.65   $194.70  
  Purchase #5 $105.46   13.368%   $119.5579   $119.56   $119.55   $119.60  
  Purchase #6 $108.47   10.438%   $119.7921   $119.79   $119.80   $119.80  
  Purchase #7 $227.29   13.202%   $257.2968   $257.30   $257.30   $257.30  
  7 purchase totals = $941.50       $1,031.0533   $1,031.06   $1,031.00   $1,031.20