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	$89.88	9.849%	$98.7323	$98.73	$98.75	$98.70
Purchase #2	$64.74	12.640%	$72.9231	$72.92	$72.90	$72.90
Purchase #3	$250.87	8.236%	$271.5317	$271.53	$271.55	$271.50
Purchase #4	$51.31	5.703%	$54.2362	$54.24	$54.25	$54.20
Purchase #5	$89.82	3.342%	$92.8218	$92.82	$92.80	$92.80
Purchase #6	$57.36	8.749%	$62.3784	$62.38	$62.40	$62.40
Purchase #7	$27.42	11.421%	$30.5516	$30.55	$30.55	$30.60
7 purchase totals =	$631.40		$683.1751	$683.17	$683.20	$683.10