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 $92.48   6.610%   $98.5929   $98.59   $98.60   $98.60  
  Purchase #2 $218.83   8.373%   $237.1526   $237.15   $237.15   $237.20  
  Purchase #3 $143.47   5.278%   $151.0423   $151.04   $151.05   $151.00  
  Purchase #4 $177.35   6.207%   $188.3581   $188.36   $188.35   $188.40  
  Purchase #5 $143.61   6.750%   $153.3037   $153.30   $153.30   $153.30  
  Purchase #6 $140.98   6.617%   $150.3086   $150.31   $150.30   $150.30  
  Purchase #7 $52.91   11.387%   $58.9349   $58.93   $58.95   $58.90  
  7 purchase totals = $969.63       $1,037.6931   $1,037.68   $1,037.70   $1,037.70