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	$233.56	3.615%	$242.0032	$242.00	$242.00	$242.00
Purchase #2	$18.51	4.788%	$19.3963	$19.40	$19.40	$19.40
Purchase #3	$120.96	8.817%	$131.625	$131.63	$131.65	$131.60
Purchase #4	$78.47	6.258%	$83.3807	$83.38	$83.40	$83.40
Purchase #5	$49.41	3.467%	$51.123	$51.12	$51.10	$51.10
Purchase #6	$175.77	6.620%	$187.406	$187.41	$187.40	$187.40
Purchase #7	$244.45	7.147%	$261.9208	$261.92	$261.90	$261.90
7 purchase totals =	$921.13		$976.8550	$976.86	$976.85	$976.80