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	$140.39	3.207%	$144.8923	$144.89	$144.90	$144.90
Purchase #2	$144.72	10.480%	$159.8867	$159.89	$159.90	$159.90
Purchase #3	$211.55	8.588%	$229.7179	$229.72	$229.70	$229.70
Purchase #4	$140.29	4.589%	$146.7279	$146.73	$146.75	$146.70
Purchase #5	$118.86	3.707%	$123.2661	$123.27	$123.25	$123.30
Purchase #6	$29.76	9.607%	$32.619	$32.62	$32.60	$32.60
Purchase #7	$81.54	8.560%	$88.5198	$88.52	$88.50	$88.50
7 purchase totals =	$867.11		$925.6297	$925.64	$925.60	$925.60