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	$223.75	3.389%	$231.3329	$231.33	$231.35	$231.30
Purchase #2	$93.72	7.397%	$100.6525	$100.65	$100.65	$100.70
Purchase #3	$86.61	3.515%	$89.6543	$89.65	$89.65	$89.70
Purchase #4	$73.27	13.655%	$83.275	$83.28	$83.30	$83.30
Purchase #5	$23.62	10.126%	$26.0118	$26.01	$26.00	$26.00
Purchase #6	$12.48	6.657%	$13.3108	$13.31	$13.30	$13.30
Purchase #7	$106.51	13.855%	$121.267	$121.27	$121.25	$121.30
7 purchase totals =	$619.96		$665.5043	$665.50	$665.50	$665.60