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	$23.90	4.135%	$24.8883	$24.89	$24.90	$24.90
Purchase #2	$85.99	4.269%	$89.6609	$89.66	$89.65	$89.70
Purchase #3	$223.94	4.574%	$234.183	$234.18	$234.20	$234.20
Purchase #4	$20.75	3.437%	$21.4632	$21.46	$21.45	$21.50
Purchase #5	$93.28	10.417%	$102.997	$103.00	$103.00	$103.00
Purchase #6	$147.74	3.244%	$152.5327	$152.53	$152.55	$152.50
Purchase #7	$36.25	12.174%	$40.6631	$40.66	$40.65	$40.70
7 purchase totals =	$631.85		$666.3882	$666.38	$666.40	$666.50