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	$197.56	6.316%	$210.0379	$210.04	$210.05	$210.00
Purchase #2	$97.90	8.696%	$106.4134	$106.41	$106.40	$106.40
Purchase #3	$247.39	11.757%	$276.4756	$276.48	$276.50	$276.50
Purchase #4	$99.30	5.804%	$105.0634	$105.06	$105.05	$105.10
Purchase #5	$30.25	7.501%	$32.5191	$32.52	$32.50	$32.50
Purchase #6	$223.92	11.466%	$249.5947	$249.59	$249.60	$249.60
Purchase #7	$106.87	8.757%	$116.2286	$116.23	$116.25	$116.20
7 purchase totals =	$1,003.19		$1,096.3327	$1,096.33	$1,096.35	$1,096.30