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	$46.54	13.375%	$52.7647	$52.76	$52.75	$52.80
Purchase #2	$72.64	5.437%	$76.5894	$76.59	$76.60	$76.60
Purchase #3	$119.45	8.735%	$129.884	$129.88	$129.90	$129.90
Purchase #4	$200.45	12.171%	$224.8468	$224.85	$224.85	$224.80
Purchase #5	$121.88	4.635%	$127.5291	$127.53	$127.55	$127.50
Purchase #6	$78.90	4.842%	$82.7203	$82.72	$82.70	$82.70
Purchase #7	$126.48	10.600%	$139.8869	$139.89	$139.90	$139.90
7 purchase totals =	$766.34		$834.2212	$834.22	$834.25	$834.20