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	$80.30	3.512%	$83.1201	$83.12	$83.10	$83.10
Purchase #2	$39.74	7.557%	$42.7432	$42.74	$42.75	$42.70
Purchase #3	$48.66	3.383%	$50.3062	$50.31	$50.30	$50.30
Purchase #4	$191.56	4.146%	$199.5021	$199.50	$199.50	$199.50
Purchase #5	$148.29	13.806%	$168.7629	$168.76	$168.75	$168.80
Purchase #6	$84.49	5.424%	$89.0727	$89.07	$89.05	$89.10
Purchase #7	$94.50	3.861%	$98.1486	$98.15	$98.15	$98.10
7 purchase totals =	$687.54		$731.6558	$731.65	$731.60	$731.60