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	$232.57	10.256%	$256.4224	$256.42	$256.40	$256.40
Purchase #2	$97.44	12.197%	$109.3248	$109.32	$109.30	$109.30
Purchase #3	$161.54	5.367%	$170.2099	$170.21	$170.20	$170.20
Purchase #4	$156.57	5.782%	$165.6229	$165.62	$165.60	$165.60
Purchase #5	$138.86	9.631%	$152.2336	$152.23	$152.25	$152.20
Purchase #6	$37.67	8.626%	$40.9194	$40.92	$40.90	$40.90
Purchase #7	$223.74	11.174%	$248.7407	$248.74	$248.75	$248.70
7 purchase totals =	$1,048.39		$1,143.4737	$1,143.46	$1,143.40	$1,143.30