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	$250.86	13.462%	$284.6308	$284.63	$284.65	$284.60
Purchase #2	$79.97	6.711%	$85.3368	$85.34	$85.35	$85.30
Purchase #3	$204.87	8.706%	$222.706	$222.71	$222.70	$222.70
Purchase #4	$139.94	3.330%	$144.6	$144.60	$144.60	$144.60
Purchase #5	$245.97	7.590%	$264.6391	$264.64	$264.65	$264.60
Purchase #6	$122.40	7.342%	$131.3866	$131.39	$131.40	$131.40
Purchase #7	$61.98	8.761%	$67.4101	$67.41	$67.40	$67.40
7 purchase totals =	$1,105.99		$1,200.7094	$1,200.72	$1,200.75	$1,200.60