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	$40.72	3.457%	$42.1277	$42.13	$42.15	$42.10
Purchase #2	$57.62	12.102%	$64.5932	$64.59	$64.60	$64.60
Purchase #3	$132.76	6.565%	$141.4757	$141.48	$141.50	$141.50
Purchase #4	$142.36	7.142%	$152.5274	$152.53	$152.55	$152.50
Purchase #5	$34.27	4.592%	$35.8437	$35.84	$35.85	$35.80
Purchase #6	$122.65	13.135%	$138.7601	$138.76	$138.75	$138.80
Purchase #7	$190.48	9.836%	$209.2156	$209.22	$209.20	$209.20
7 purchase totals =	$720.86		$784.5434	$784.55	$784.60	$784.50