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	$163.45	10.311%	$180.3033	$180.30	$180.30	$180.30
Purchase #2	$60.48	13.174%	$68.4476	$68.45	$68.45	$68.40
Purchase #3	$26.88	3.251%	$27.7539	$27.75	$27.75	$27.80
Purchase #4	$153.40	8.488%	$166.4206	$166.42	$166.40	$166.40
Purchase #5	$75.56	10.615%	$83.5807	$83.58	$83.60	$83.60
Purchase #6	$51.98	10.317%	$57.3428	$57.34	$57.35	$57.30
Purchase #7	$40.46	12.516%	$45.524	$45.52	$45.50	$45.50
7 purchase totals =	$572.21		$629.3729	$629.36	$629.35	$629.30