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	$166.74	7.505%	$179.2538	$179.25	$179.25	$179.30
Purchase #2	$185.78	3.291%	$191.894	$191.89	$191.90	$191.90
Purchase #3	$243.29	12.351%	$273.3387	$273.34	$273.35	$273.30
Purchase #4	$214.61	8.432%	$232.7059	$232.71	$232.70	$232.70
Purchase #5	$12.48	13.227%	$14.1307	$14.13	$14.15	$14.10
Purchase #6	$165.51	8.539%	$179.6429	$179.64	$179.65	$179.60
Purchase #7	$190.90	9.732%	$209.4784	$209.48	$209.50	$209.50
7 purchase totals =	$1,179.31		$1,280.4444	$1,280.44	$1,280.50	$1,280.40