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	$51.53	7.843%	$55.5715	$55.57	$55.55	$55.60
Purchase #2	$228.87	8.215%	$247.6717	$247.67	$247.65	$247.70
Purchase #3	$59.61	13.709%	$67.7819	$67.78	$67.80	$67.80
Purchase #4	$99.78	5.271%	$105.0394	$105.04	$105.05	$105.00
Purchase #5	$133.61	13.421%	$151.5418	$151.54	$151.55	$151.50
Purchase #6	$71.62	11.261%	$79.6851	$79.69	$79.70	$79.70
Purchase #7	$140.49	4.464%	$146.7615	$146.76	$146.75	$146.80
7 purchase totals =	$785.51		$854.0529	$854.05	$854.05	$854.10