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	$113.66	13.803%	$129.3485	$129.35	$129.35	$129.30
Purchase #2	$146.86	6.714%	$156.7202	$156.72	$156.70	$156.70
Purchase #3	$121.82	7.643%	$131.1307	$131.13	$131.15	$131.10
Purchase #4	$116.53	5.512%	$122.9531	$122.95	$122.95	$123.00
Purchase #5	$54.54	8.184%	$59.0036	$59.00	$59.00	$59.00
Purchase #6	$98.33	12.259%	$110.3843	$110.38	$110.40	$110.40
Purchase #7	$99.78	9.431%	$109.1903	$109.19	$109.20	$109.20
7 purchase totals =	$751.52		$818.7307	$818.72	$818.75	$818.70