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	$56.51	4.580%	$59.0982	$59.10	$59.10	$59.10
Purchase #2	$229.98	13.669%	$261.416	$261.42	$261.40	$261.40
Purchase #3	$120.50	5.777%	$127.4613	$127.46	$127.45	$127.50
Purchase #4	$157.95	8.845%	$171.9207	$171.92	$171.90	$171.90
Purchase #5	$105.33	4.624%	$110.2005	$110.20	$110.20	$110.20
Purchase #6	$240.64	12.203%	$270.0053	$270.01	$270.00	$270.00
Purchase #7	$248.36	3.123%	$256.1163	$256.12	$256.10	$256.10
7 purchase totals =	$1,159.27		$1,256.2183	$1,256.23	$1,256.15	$1,256.20