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	$121.46	7.664%	$130.7687	$130.77	$130.75	$130.80
Purchase #2	$83.38	7.250%	$89.4251	$89.43	$89.45	$89.40
Purchase #3	$228.63	11.114%	$254.0399	$254.04	$254.05	$254.00
Purchase #4	$156.40	12.826%	$176.4599	$176.46	$176.45	$176.50
Purchase #5	$78.39	6.170%	$83.2267	$83.23	$83.25	$83.20
Purchase #6	$31.98	9.237%	$34.934	$34.93	$34.95	$34.90
Purchase #7	$43.58	11.174%	$48.4496	$48.45	$48.45	$48.40
7 purchase totals =	$743.82		$817.3039	$817.31	$817.35	$817.20