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	$98.84	12.851%	$111.5419	$111.54	$111.55	$111.50
Purchase #2	$91.51	10.401%	$101.028	$101.03	$101.05	$101.00
Purchase #3	$6.87	6.283%	$7.3016	$7.30	$7.30	$7.30
Purchase #4	$123.51	13.287%	$139.9208	$139.92	$139.90	$139.90
Purchase #5	$26.39	6.691%	$28.1558	$28.16	$28.15	$28.20
Purchase #6	$59.69	9.760%	$65.5157	$65.52	$65.50	$65.50
Purchase #7	$106.42	6.144%	$112.9584	$112.96	$112.95	$113.00
7 purchase totals =	$513.23		$566.4222	$566.43	$566.40	$566.40