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	$27.63	12.347%	$31.0415	$31.04	$31.05	$31.00
Purchase #2	$16.44	11.369%	$18.3091	$18.31	$18.30	$18.30
Purchase #3	$124.39	5.490%	$131.219	$131.22	$131.20	$131.20
Purchase #4	$88.67	12.181%	$99.4709	$99.47	$99.45	$99.50
Purchase #5	$57.47	6.325%	$61.105	$61.11	$61.10	$61.10
Purchase #6	$73.72	10.614%	$81.5446	$81.54	$81.55	$81.50
Purchase #7	$24.89	7.810%	$26.8339	$26.83	$26.85	$26.80
7 purchase totals =	$413.21		$449.5240	$449.52	$449.50	$449.40