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	$37.65	12.359%	$42.3032	$42.30	$42.30	$42.30
Purchase #2	$142.63	12.834%	$160.9351	$160.94	$160.95	$160.90
Purchase #3	$175.32	13.727%	$199.3862	$199.39	$199.40	$199.40
Purchase #4	$200.43	10.262%	$220.9981	$221.00	$221.00	$221.00
Purchase #5	$137.91	5.147%	$145.0082	$145.01	$145.00	$145.00
Purchase #6	$37.63	13.492%	$42.707	$42.71	$42.70	$42.70
Purchase #7	$41.84	6.524%	$44.5696	$44.57	$44.55	$44.60
7 purchase totals =	$773.41		$855.9074	$855.92	$855.90	$855.90