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	$208.69	6.474%	$222.2006	$222.20	$222.20	$222.20
Purchase #2	$243.90	13.858%	$277.6997	$277.70	$277.70	$277.70
Purchase #3	$70.98	12.814%	$80.0754	$80.08	$80.10	$80.10
Purchase #4	$43.41	4.383%	$45.3127	$45.31	$45.30	$45.30
Purchase #5	$222.30	4.346%	$231.9612	$231.96	$231.95	$232.00
Purchase #6	$129.54	11.271%	$144.1405	$144.14	$144.15	$144.10
Purchase #7	$172.46	9.276%	$188.4574	$188.46	$188.45	$188.50
7 purchase totals =	$1,091.28		$1,189.8475	$1,189.85	$1,189.85	$1,189.90