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	$84.75	5.241%	$89.1917	$89.19	$89.20	$89.20
Purchase #2	$29.95	11.260%	$33.3224	$33.32	$33.30	$33.30
Purchase #3	$79.89	6.645%	$85.1987	$85.20	$85.20	$85.20
Purchase #4	$114.60	8.210%	$124.0087	$124.01	$124.00	$124.00
Purchase #5	$189.67	3.575%	$196.4507	$196.45	$196.45	$196.50
Purchase #6	$42.49	9.115%	$46.363	$46.36	$46.35	$46.40
Purchase #7	$80.36	13.142%	$90.9209	$90.92	$90.90	$90.90
7 purchase totals =	$621.71		$665.4561	$665.45	$665.40	$665.50