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	$155.38	3.118%	$160.2247	$160.22	$160.20	$160.20
Purchase #2	$175.85	6.705%	$187.6407	$187.64	$187.65	$187.60
Purchase #3	$39.46	8.358%	$42.7581	$42.76	$42.75	$42.80
Purchase #4	$89.51	3.524%	$92.6643	$92.66	$92.65	$92.70
Purchase #5	$6.36	3.431%	$6.5782	$6.58	$6.60	$6.60
Purchase #6	$173.97	11.853%	$194.5907	$194.59	$194.60	$194.60
Purchase #7	$55.53	6.271%	$59.0123	$59.01	$59.00	$59.00
7 purchase totals =	$696.06		$743.4690	$743.46	$743.45	$743.50