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	$231.88	3.589%	$240.2022	$240.20	$240.20	$240.20
Purchase #2	$142.52	6.400%	$151.6413	$151.64	$151.65	$151.60
Purchase #3	$159.48	6.427%	$169.7298	$169.73	$169.75	$169.70
Purchase #4	$194.28	9.685%	$213.096	$213.10	$213.10	$213.10
Purchase #5	$250.96	4.230%	$261.5756	$261.58	$261.60	$261.60
Purchase #6	$102.47	10.740%	$113.4753	$113.48	$113.50	$113.50
Purchase #7	$138.32	9.526%	$151.4964	$151.50	$151.50	$151.50
7 purchase totals =	$1,219.91		$1,301.2166	$1,301.23	$1,301.30	$1,301.20