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	$79.84	12.501%	$89.8208	$89.82	$89.80	$89.80
Purchase #2	$78.86	8.431%	$85.5087	$85.51	$85.50	$85.50
Purchase #3	$146.36	5.367%	$154.2151	$154.22	$154.20	$154.20
Purchase #4	$97.95	5.832%	$103.6624	$103.66	$103.65	$103.70
Purchase #5	$75.93	4.438%	$79.2998	$79.30	$79.30	$79.30
Purchase #6	$42.43	4.126%	$44.1807	$44.18	$44.20	$44.20
Purchase #7	$97.47	13.205%	$110.3409	$110.34	$110.35	$110.30
7 purchase totals =	$618.84		$667.0284	$667.03	$667.00	$667.00