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	$155.38	12.220%	$174.3674	$174.37	$174.35	$174.40
Purchase #2	$99.28	3.187%	$102.4441	$102.44	$102.45	$102.40
Purchase #3	$48.95	8.863%	$53.2884	$53.29	$53.30	$53.30
Purchase #4	$95.61	4.488%	$99.901	$99.90	$99.90	$99.90
Purchase #5	$93.34	7.305%	$100.1585	$100.16	$100.15	$100.20
Purchase #6	$191.83	10.469%	$211.9127	$211.91	$211.90	$211.90
Purchase #7	$59.51	8.367%	$64.4892	$64.49	$64.50	$64.50
7 purchase totals =	$743.90		$806.5613	$806.56	$806.55	$806.60