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	$89.83	11.869%	$100.4919	$100.49	$100.50	$100.50
Purchase #2	$127.63	12.301%	$143.3298	$143.33	$143.35	$143.30
Purchase #3	$212.29	9.394%	$232.2325	$232.23	$232.25	$232.20
Purchase #4	$175.85	3.721%	$182.3934	$182.39	$182.40	$182.40
Purchase #5	$233.32	9.838%	$256.274	$256.27	$256.25	$256.30
Purchase #6	$165.46	3.385%	$171.0608	$171.06	$171.05	$171.10
Purchase #7	$140.82	13.717%	$160.1363	$160.14	$160.15	$160.10
7 purchase totals =	$1,145.20		$1,245.9187	$1,245.91	$1,245.95	$1,245.90