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	$82.49	4.461%	$86.1699	$86.17	$86.15	$86.20
Purchase #2	$156.93	4.828%	$164.5066	$164.51	$164.50	$164.50
Purchase #3	$106.66	6.234%	$113.3092	$113.31	$113.30	$113.30
Purchase #4	$37.55	7.449%	$40.3471	$40.35	$40.35	$40.30
Purchase #5	$109.77	4.102%	$114.2728	$114.27	$114.25	$114.30
Purchase #6	$44.53	12.446%	$50.0722	$50.07	$50.05	$50.10
Purchase #7	$68.43	5.745%	$72.3613	$72.36	$72.35	$72.40
7 purchase totals =	$606.36		$641.0391	$641.04	$640.95	$641.10