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	$186.51	5.361%	$196.5088	$196.51	$196.50	$196.50
Purchase #2	$105.77	9.850%	$116.1883	$116.19	$116.20	$116.20
Purchase #3	$79.87	6.670%	$85.1973	$85.20	$85.20	$85.20
Purchase #4	$237.82	11.224%	$264.5129	$264.51	$264.50	$264.50
Purchase #5	$16.46	8.845%	$17.9159	$17.92	$17.90	$17.90
Purchase #6	$47.67	13.281%	$54.0011	$54.00	$54.00	$54.00
Purchase #7	$167.42	11.586%	$186.8173	$186.82	$186.80	$186.80
7 purchase totals =	$841.52		$921.1416	$921.15	$921.10	$921.10