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	$247.33	9.411%	$270.6062	$270.61	$270.60	$270.60
Purchase #2	$61.77	5.695%	$65.2878	$65.29	$65.30	$65.30
Purchase #3	$135.90	6.438%	$144.6492	$144.65	$144.65	$144.60
Purchase #4	$105.95	3.388%	$109.5396	$109.54	$109.55	$109.50
Purchase #5	$233.42	13.655%	$265.2935	$265.29	$265.30	$265.30
Purchase #6	$111.51	4.496%	$116.5235	$116.52	$116.50	$116.50
Purchase #7	$126.72	3.375%	$130.9968	$131.00	$131.00	$131.00
7 purchase totals =	$1,022.60		$1,102.8966	$1,102.90	$1,102.90	$1,102.80