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	$207.73	10.383%	$229.2986	$229.30	$229.30	$229.30
Purchase #2	$96.55	3.369%	$99.8028	$99.80	$99.80	$99.80
Purchase #3	$130.46	7.754%	$140.5759	$140.58	$140.60	$140.60
Purchase #4	$165.56	11.544%	$184.6722	$184.67	$184.65	$184.70
Purchase #5	$148.72	5.434%	$156.8014	$156.80	$156.80	$156.80
Purchase #6	$57.81	13.688%	$65.723	$65.72	$65.70	$65.70
Purchase #7	$57.96	6.700%	$61.8433	$61.84	$61.85	$61.80
7 purchase totals =	$864.79		$938.7172	$938.71	$938.70	$938.70