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	$207.83	13.702%	$236.3069	$236.31	$236.30	$236.30
Purchase #2	$173.75	10.526%	$192.0389	$192.04	$192.05	$192.00
Purchase #3	$196.76	13.581%	$223.482	$223.48	$223.50	$223.50
Purchase #4	$49.46	13.480%	$56.1272	$56.13	$56.15	$56.10
Purchase #5	$36.51	3.742%	$37.8762	$37.88	$37.90	$37.90
Purchase #6	$139.25	9.333%	$152.2462	$152.25	$152.25	$152.20
Purchase #7	$88.39	12.786%	$99.6915	$99.69	$99.70	$99.70
7 purchase totals =	$891.95		$997.7689	$997.78	$997.85	$997.70