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	$75.62	6.732%	$80.7107	$80.71	$80.70	$80.70
Purchase #2	$145.25	4.227%	$151.3897	$151.39	$151.40	$151.40
Purchase #3	$228.80	6.754%	$244.2532	$244.25	$244.25	$244.30
Purchase #4	$30.86	11.457%	$34.3956	$34.40	$34.40	$34.40
Purchase #5	$234.84	12.552%	$264.3171	$264.32	$264.30	$264.30
Purchase #6	$54.72	8.612%	$59.4325	$59.43	$59.45	$59.40
Purchase #7	$242.83	6.224%	$257.9437	$257.94	$257.95	$257.90
7 purchase totals =	$1,012.92		$1,092.4425	$1,092.44	$1,092.45	$1,092.40