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	$159.98	3.370%	$165.3713	$165.37	$165.35	$165.40
Purchase #2	$205.45	8.799%	$223.5275	$223.53	$223.55	$223.50
Purchase #3	$137.44	4.461%	$143.5712	$143.57	$143.55	$143.60
Purchase #4	$200.94	10.525%	$222.0889	$222.09	$222.10	$222.10
Purchase #5	$130.56	8.310%	$141.4095	$141.41	$141.40	$141.40
Purchase #6	$96.34	3.748%	$99.9508	$99.95	$99.95	$100.00
Purchase #7	$80.46	12.316%	$90.3695	$90.37	$90.35	$90.40
7 purchase totals =	$1,011.17		$1,086.2887	$1,086.29	$1,086.25	$1,086.40