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	$153.69	12.226%	$172.4801	$172.48	$172.50	$172.50
Purchase #2	$67.29	6.132%	$71.4162	$71.42	$71.40	$71.40
Purchase #3	$182.87	3.575%	$189.4076	$189.41	$189.40	$189.40
Purchase #4	$42.36	11.793%	$47.3555	$47.36	$47.35	$47.40
Purchase #5	$43.49	4.401%	$45.404	$45.40	$45.40	$45.40
Purchase #6	$142.80	3.341%	$147.5709	$147.57	$147.55	$147.60
Purchase #7	$112.51	8.657%	$122.25	$122.25	$122.25	$122.30
7 purchase totals =	$745.01		$795.8843	$795.89	$795.85	$796.00