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	$248.96	9.866%	$273.5224	$273.52	$273.50	$273.50
Purchase #2	$127.72	11.215%	$142.0438	$142.04	$142.05	$142.00
Purchase #3	$31.59	6.329%	$33.5893	$33.59	$33.60	$33.60
Purchase #4	$219.54	12.310%	$246.5654	$246.57	$246.55	$246.60
Purchase #5	$124.46	13.783%	$141.6143	$141.61	$141.60	$141.60
Purchase #6	$53.73	10.139%	$59.1777	$59.18	$59.20	$59.20
Purchase #7	$182.51	13.666%	$207.4518	$207.45	$207.45	$207.50
7 purchase totals =	$988.51		$1,103.9647	$1,103.96	$1,103.95	$1,104.00