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	$89.82	11.512%	$100.1601	$100.16	$100.15	$100.20
Purchase #2	$79.53	12.417%	$89.4052	$89.41	$89.40	$89.40
Purchase #3	$18.77	8.566%	$20.3778	$20.38	$20.40	$20.40
Purchase #4	$237.61	4.321%	$247.8771	$247.88	$247.90	$247.90
Purchase #5	$34.25	10.227%	$37.7527	$37.75	$37.75	$37.80
Purchase #6	$46.69	8.719%	$50.7609	$50.76	$50.75	$50.80
Purchase #7	$51.89	11.814%	$58.0203	$58.02	$58.00	$58.00
7 purchase totals =	$558.56		$604.3541	$604.36	$604.35	$604.50