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	$243.95	12.773%	$275.1097	$275.11	$275.10	$275.10
Purchase #2	$125.48	7.539%	$134.9399	$134.94	$134.95	$134.90
Purchase #3	$152.37	7.832%	$164.3036	$164.30	$164.30	$164.30
Purchase #4	$75.75	12.623%	$85.3119	$85.31	$85.30	$85.30
Purchase #5	$10.77	10.679%	$11.9201	$11.92	$11.90	$11.90
Purchase #6	$40.77	12.358%	$45.8084	$45.81	$45.80	$45.80
Purchase #7	$72.59	12.371%	$81.5701	$81.57	$81.55	$81.60
7 purchase totals =	$721.68		$798.9637	$798.96	$798.90	$798.90