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	$53.30	12.201%	$59.8031	$59.80	$59.80	$59.80
Purchase #2	$191.88	8.404%	$208.0056	$208.01	$208.00	$208.00
Purchase #3	$27.71	7.782%	$29.8664	$29.87	$29.85	$29.90
Purchase #4	$81.82	9.675%	$89.7361	$89.74	$89.75	$89.70
Purchase #5	$176.87	8.702%	$192.2612	$192.26	$192.25	$192.30
Purchase #6	$18.25	8.818%	$19.8593	$19.86	$19.85	$19.90
Purchase #7	$61.68	9.489%	$67.5328	$67.53	$67.55	$67.50
7 purchase totals =	$611.51		$667.0645	$667.07	$667.05	$667.10