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	$71.67	12.344%	$80.5169	$80.52	$80.50	$80.50
Purchase #2	$146.80	6.623%	$156.5226	$156.52	$156.50	$156.50
Purchase #3	$71.81	3.765%	$74.5136	$74.51	$74.50	$74.50
Purchase #4	$64.29	11.220%	$71.5033	$71.50	$71.50	$71.50
Purchase #5	$53.61	10.157%	$59.0552	$59.06	$59.05	$59.10
Purchase #6	$223.31	12.590%	$251.4247	$251.42	$251.40	$251.40
Purchase #7	$110.41	9.391%	$120.7786	$120.78	$120.80	$120.80
7 purchase totals =	$741.90		$814.3149	$814.31	$814.25	$814.30