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	$20.98	6.111%	$22.2621	$22.26	$22.25	$22.30
Purchase #2	$38.51	8.215%	$41.6736	$41.67	$41.65	$41.70
Purchase #3	$37.89	5.866%	$40.1126	$40.11	$40.10	$40.10
Purchase #4	$185.89	6.817%	$198.5621	$198.56	$198.55	$198.60
Purchase #5	$122.62	11.866%	$137.1701	$137.17	$137.15	$137.20
Purchase #6	$42.29	7.498%	$45.4609	$45.46	$45.45	$45.50
Purchase #7	$60.25	8.280%	$65.2387	$65.24	$65.25	$65.20
7 purchase totals =	$508.43		$550.4801	$550.47	$550.40	$550.60