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	$239.77	9.812%	$263.2962	$263.30	$263.30	$263.30
Purchase #2	$103.76	7.518%	$111.5607	$111.56	$111.55	$111.60
Purchase #3	$15.69	3.594%	$16.2539	$16.25	$16.25	$16.30
Purchase #4	$211.48	8.465%	$229.3818	$229.38	$229.40	$229.40
Purchase #5	$27.90	4.575%	$29.1764	$29.18	$29.20	$29.20
Purchase #6	$86.25	4.845%	$90.4288	$90.43	$90.45	$90.40
Purchase #7	$27.76	11.498%	$30.9518	$30.95	$30.95	$31.00
7 purchase totals =	$712.61		$771.0496	$771.05	$771.10	$771.20