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 $92.63   3.654%   $96.0147   $96.01   $96.00   $96.00  
  Purchase #2 $183.81   3.123%   $189.5504   $189.55   $189.55   $189.60  
  Purchase #3 $55.95   4.439%   $58.4336   $58.43   $58.45   $58.40  
  Purchase #4 $215.99   11.395%   $240.6021   $240.60   $240.60   $240.60  
  Purchase #5 $105.50   12.629%   $118.8236   $118.82   $118.80   $118.80  
  Purchase #6 $48.78   11.163%   $54.2253   $54.23   $54.25   $54.20  
  Purchase #7 $172.66   8.397%   $187.1583   $187.16   $187.15   $187.20  
  7 purchase totals = $875.32       $944.8080   $944.80   $944.80   $944.80