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	$230.33	5.728%	$243.5233	$243.52	$243.50	$243.50
Purchase #2	$81.70	9.819%	$89.7221	$89.72	$89.70	$89.70
Purchase #3	$85.84	5.700%	$90.7329	$90.73	$90.75	$90.70
Purchase #4	$182.86	5.552%	$193.0124	$193.01	$193.00	$193.00
Purchase #5	$227.62	7.838%	$245.4609	$245.46	$245.45	$245.50
Purchase #6	$79.87	11.323%	$88.9137	$88.91	$88.90	$88.90
Purchase #7	$54.92	3.109%	$56.6275	$56.63	$56.65	$56.60
7 purchase totals =	$943.14		$1,007.9928	$1,007.98	$1,007.95	$1,007.90