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	$54.94	4.735%	$57.5414	$57.54	$57.55	$57.50
Purchase #2	$191.84	13.403%	$217.5523	$217.55	$217.55	$217.60
Purchase #3	$71.89	6.152%	$76.3127	$76.31	$76.30	$76.30
Purchase #4	$81.55	9.266%	$89.1064	$89.11	$89.10	$89.10
Purchase #5	$158.29	6.263%	$168.2037	$168.20	$168.20	$168.20
Purchase #6	$145.89	3.704%	$151.2938	$151.29	$151.30	$151.30
Purchase #7	$75.73	11.388%	$84.3541	$84.35	$84.35	$84.40
7 purchase totals =	$780.13		$844.3644	$844.35	$844.35	$844.40