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	$142.68	6.118%	$151.4092	$151.41	$151.40	$151.40
Purchase #2	$158.73	4.113%	$165.2586	$165.26	$165.25	$165.30
Purchase #3	$137.74	10.512%	$152.2192	$152.22	$152.20	$152.20
Purchase #4	$153.95	11.434%	$171.5526	$171.55	$171.55	$171.60
Purchase #5	$35.87	6.672%	$38.2632	$38.26	$38.25	$38.30
Purchase #6	$239.99	11.855%	$268.4408	$268.44	$268.45	$268.40
Purchase #7	$28.84	9.141%	$31.4763	$31.48	$31.50	$31.50
7 purchase totals =	$897.80		$978.6199	$978.62	$978.60	$978.70