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	$127.34	12.497%	$143.2537	$143.25	$143.25	$143.30
Purchase #2	$113.31	9.361%	$123.9169	$123.92	$123.90	$123.90
Purchase #3	$48.72	9.812%	$53.5004	$53.50	$53.50	$53.50
Purchase #4	$8.76	7.318%	$9.4011	$9.40	$9.40	$9.40
Purchase #5	$220.53	10.293%	$243.2292	$243.23	$243.25	$243.20
Purchase #6	$111.74	12.830%	$126.0762	$126.08	$126.10	$126.10
Purchase #7	$35.40	13.290%	$40.1047	$40.10	$40.10	$40.10
7 purchase totals =	$665.80		$739.4822	$739.48	$739.50	$739.50