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	$186.38	10.234%	$205.4541	$205.45	$205.45	$205.50
Purchase #2	$83.44	7.331%	$89.557	$89.56	$89.55	$89.60
Purchase #3	$23.79	7.466%	$25.5662	$25.57	$25.55	$25.60
Purchase #4	$25.39	5.596%	$26.8108	$26.81	$26.80	$26.80
Purchase #5	$139.46	6.301%	$148.2474	$148.25	$148.25	$148.20
Purchase #6	$121.59	5.216%	$127.9321	$127.93	$127.95	$127.90
Purchase #7	$22.90	8.361%	$24.8147	$24.81	$24.80	$24.80
7 purchase totals =	$602.95		$648.3823	$648.38	$648.35	$648.40