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	$190.75	6.592%	$203.3242	$203.32	$203.30	$203.30
Purchase #2	$64.83	9.225%	$70.8106	$70.81	$70.80	$70.80
Purchase #3	$243.56	13.574%	$276.6208	$276.62	$276.60	$276.60
Purchase #4	$26.27	4.594%	$27.4768	$27.48	$27.50	$27.50
Purchase #5	$188.39	13.807%	$214.401	$214.40	$214.40	$214.40
Purchase #6	$120.89	8.557%	$131.2346	$131.23	$131.25	$131.20
Purchase #7	$184.65	8.375%	$200.1144	$200.11	$200.10	$200.10
7 purchase totals =	$1,019.34		$1,123.9824	$1,123.97	$1,123.95	$1,123.90