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	$120.28	3.816%	$124.8699	$124.87	$124.85	$124.90
Purchase #2	$30.78	8.143%	$33.2864	$33.29	$33.30	$33.30
Purchase #3	$123.48	12.687%	$139.1459	$139.15	$139.15	$139.10
Purchase #4	$171.80	12.329%	$192.9812	$192.98	$193.00	$193.00
Purchase #5	$215.32	3.310%	$222.4471	$222.45	$222.45	$222.40
Purchase #6	$60.25	8.441%	$65.3357	$65.34	$65.35	$65.30
Purchase #7	$50.44	11.726%	$56.3546	$56.35	$56.35	$56.40
7 purchase totals =	$772.35		$834.4208	$834.43	$834.45	$834.40