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	$20.59	8.103%	$22.2584	$22.26	$22.25	$22.30
Purchase #2	$43.48	13.742%	$49.455	$49.46	$49.45	$49.50
Purchase #3	$91.37	7.434%	$98.1624	$98.16	$98.15	$98.20
Purchase #4	$88.73	8.626%	$96.3838	$96.38	$96.40	$96.40
Purchase #5	$133.34	9.827%	$146.4433	$146.44	$146.45	$146.40
Purchase #6	$233.51	9.311%	$255.2521	$255.25	$255.25	$255.30
Purchase #7	$198.62	12.167%	$222.7861	$222.79	$222.80	$222.80
7 purchase totals =	$809.64		$890.7411	$890.74	$890.75	$890.90