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	$229.83	9.171%	$250.9077	$250.91	$250.90	$250.90
Purchase #2	$232.55	3.385%	$240.4218	$240.42	$240.40	$240.40
Purchase #3	$83.74	6.675%	$89.3296	$89.33	$89.35	$89.30
Purchase #4	$54.84	12.751%	$61.8326	$61.83	$61.85	$61.80
Purchase #5	$42.96	6.756%	$45.8624	$45.86	$45.85	$45.90
Purchase #6	$74.78	13.726%	$85.0443	$85.04	$85.05	$85.00
Purchase #7	$131.48	10.428%	$145.1907	$145.19	$145.20	$145.20
7 purchase totals =	$850.18		$918.5891	$918.58	$918.60	$918.50