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	$21.68	12.431%	$24.375	$24.38	$24.40	$24.40
Purchase #2	$164.80	4.616%	$172.4072	$172.41	$172.40	$172.40
Purchase #3	$180.91	9.608%	$198.2918	$198.29	$198.30	$198.30
Purchase #4	$42.59	11.519%	$47.4959	$47.50	$47.50	$47.50
Purchase #5	$89.84	10.533%	$99.3028	$99.30	$99.30	$99.30
Purchase #6	$178.41	7.212%	$191.2769	$191.28	$191.30	$191.30
Purchase #7	$129.85	12.468%	$146.0397	$146.04	$146.05	$146.00
7 purchase totals =	$808.08		$879.1893	$879.20	$879.25	$879.20