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	$32.57	9.175%	$35.5583	$35.56	$35.55	$35.60
Purchase #2	$142.76	3.333%	$147.5182	$147.52	$147.50	$147.50
Purchase #3	$89.38	8.206%	$96.7145	$96.71	$96.70	$96.70
Purchase #4	$209.79	5.743%	$221.8382	$221.84	$221.85	$221.80
Purchase #5	$244.59	4.760%	$256.2325	$256.23	$256.25	$256.20
Purchase #6	$61.27	13.501%	$69.5421	$69.54	$69.55	$69.50
Purchase #7	$60.97	4.387%	$63.6448	$63.64	$63.65	$63.60
7 purchase totals =	$841.33		$891.0486	$891.04	$891.05	$890.90