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	$227.87	12.250%	$255.7841	$255.78	$255.80	$255.80
Purchase #2	$49.93	7.316%	$53.5829	$53.58	$53.60	$53.60
Purchase #3	$139.71	8.339%	$151.3604	$151.36	$151.35	$151.40
Purchase #4	$136.41	7.322%	$146.3979	$146.40	$146.40	$146.40
Purchase #5	$25.46	9.558%	$27.8935	$27.89	$27.90	$27.90
Purchase #6	$203.36	9.305%	$222.2826	$222.28	$222.30	$222.30
Purchase #7	$16.39	3.199%	$16.9143	$16.91	$16.90	$16.90
7 purchase totals =	$799.13		$874.2157	$874.20	$874.25	$874.30