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	$37.60	11.825%	$42.0462	$42.05	$42.05	$42.00
Purchase #2	$243.67	13.641%	$276.909	$276.91	$276.90	$276.90
Purchase #3	$146.28	10.757%	$162.0153	$162.02	$162.00	$162.00
Purchase #4	$101.66	12.558%	$114.4265	$114.43	$114.45	$114.40
Purchase #5	$155.31	12.781%	$175.1602	$175.16	$175.15	$175.20
Purchase #6	$247.42	6.866%	$264.4079	$264.41	$264.40	$264.40
Purchase #7	$20.30	7.712%	$21.8655	$21.87	$21.85	$21.90
7 purchase totals =	$952.24		$1,056.8306	$1,056.85	$1,056.80	$1,056.80