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	$53.48	3.435%	$55.317	$55.32	$55.30	$55.30
Purchase #2	$32.71	13.324%	$37.0683	$37.07	$37.05	$37.10
Purchase #3	$83.90	7.130%	$89.8821	$89.88	$89.90	$89.90
Purchase #4	$176.94	3.593%	$183.2975	$183.30	$183.30	$183.30
Purchase #5	$29.97	6.191%	$31.8254	$31.83	$31.85	$31.80
Purchase #6	$240.26	4.559%	$251.2135	$251.21	$251.20	$251.20
Purchase #7	$28.82	8.774%	$31.3487	$31.35	$31.35	$31.30
7 purchase totals =	$646.08		$679.9525	$679.96	$679.95	$679.90