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	$133.85	10.180%	$147.4759	$147.48	$147.50	$147.50
Purchase #2	$58.58	11.308%	$65.2042	$65.20	$65.20	$65.20
Purchase #3	$65.98	8.515%	$71.5982	$71.60	$71.60	$71.60
Purchase #4	$99.45	6.241%	$105.6567	$105.66	$105.65	$105.70
Purchase #5	$125.90	9.184%	$137.4627	$137.46	$137.45	$137.50
Purchase #6	$172.37	5.113%	$181.1833	$181.18	$181.20	$181.20
Purchase #7	$89.74	13.257%	$101.6368	$101.64	$101.65	$101.60
7 purchase totals =	$745.87		$810.2178	$810.22	$810.25	$810.30