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	$48.55	13.535%	$55.1212	$55.12	$55.10	$55.10
Purchase #2	$181.35	10.698%	$200.7508	$200.75	$200.75	$200.80
Purchase #3	$92.59	13.310%	$104.9137	$104.91	$104.90	$104.90
Purchase #4	$87.86	13.677%	$99.8766	$99.88	$99.90	$99.90
Purchase #5	$39.44	8.586%	$42.8263	$42.83	$42.85	$42.80
Purchase #6	$237.33	11.802%	$265.3397	$265.34	$265.35	$265.30
Purchase #7	$222.42	3.470%	$230.138	$230.14	$230.15	$230.10
7 purchase totals =	$909.54		$998.9663	$998.97	$999.00	$998.90