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	$82.81	10.104%	$91.1771	$91.18	$91.20	$91.20
Purchase #2	$179.52	11.226%	$199.6729	$199.67	$199.65	$199.70
Purchase #3	$232.42	13.703%	$264.2685	$264.27	$264.25	$264.30
Purchase #4	$61.45	4.484%	$64.2054	$64.21	$64.20	$64.20
Purchase #5	$131.59	5.809%	$139.2341	$139.23	$139.25	$139.20
Purchase #6	$243.42	3.187%	$251.1778	$251.18	$251.20	$251.20
Purchase #7	$63.76	12.153%	$71.5088	$71.51	$71.50	$71.50
7 purchase totals =	$994.97		$1,081.2446	$1,081.25	$1,081.25	$1,081.30