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	$120.91	5.283%	$127.2977	$127.30	$127.30	$127.30
Purchase #2	$146.88	12.280%	$164.9169	$164.92	$164.90	$164.90
Purchase #3	$221.83	4.801%	$232.4801	$232.48	$232.50	$232.50
Purchase #4	$31.74	3.783%	$32.9407	$32.94	$32.95	$32.90
Purchase #5	$168.46	7.197%	$180.5841	$180.58	$180.60	$180.60
Purchase #6	$198.59	7.280%	$213.0474	$213.05	$213.05	$213.00
Purchase #7	$51.83	10.515%	$57.2799	$57.28	$57.30	$57.30
7 purchase totals =	$940.24		$1,008.5468	$1,008.55	$1,008.60	$1,008.50