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 $88.95   8.491%   $96.5027   $96.50   $96.50   $96.50  
  Purchase #2 $214.33   12.399%   $240.9048   $240.90   $240.90   $240.90  
  Purchase #3 $236.67   3.705%   $245.4386   $245.44   $245.45   $245.40  
  Purchase #4 $71.29   10.397%   $78.702   $78.70   $78.70   $78.70  
  Purchase #5 $193.76   3.224%   $200.0068   $200.01   $200.00   $200.00  
  Purchase #6 $67.55   3.132%   $69.6657   $69.67   $69.65   $69.70  
  Purchase #7 $129.81   7.291%   $139.2744   $139.27   $139.25   $139.30  
  7 purchase totals = $1,002.36       $1,070.4950   $1,070.49   $1,070.45   $1,070.50