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	$36.34	13.179%	$41.1292	$41.13	$41.15	$41.10
Purchase #2	$171.79	11.654%	$191.8104	$191.81	$191.80	$191.80
Purchase #3	$130.90	8.111%	$141.5173	$141.52	$141.50	$141.50
Purchase #4	$137.56	8.691%	$149.5153	$149.52	$149.50	$149.50
Purchase #5	$207.50	6.653%	$221.305	$221.31	$221.30	$221.30
Purchase #6	$146.65	8.161%	$158.6181	$158.62	$158.60	$158.60
Purchase #7	$59.42	3.188%	$61.3143	$61.31	$61.30	$61.30
7 purchase totals =	$890.16		$965.2096	$965.22	$965.15	$965.10