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	$223.33	13.685%	$253.8927	$253.89	$253.90	$253.90
Purchase #2	$115.92	8.291%	$125.5309	$125.53	$125.55	$125.50
Purchase #3	$56.46	8.155%	$61.0643	$61.06	$61.05	$61.10
Purchase #4	$179.68	3.102%	$185.2537	$185.25	$185.25	$185.30
Purchase #5	$102.61	8.229%	$111.0538	$111.05	$111.05	$111.10
Purchase #6	$61.54	10.448%	$67.9697	$67.97	$67.95	$68.00
Purchase #7	$30.86	13.625%	$35.0647	$35.06	$35.05	$35.10
7 purchase totals =	$770.40		$839.8298	$839.81	$839.80	$840.00