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	$80.44	12.710%	$90.6639	$90.66	$90.65	$90.70
Purchase #2	$52.33	9.446%	$57.2731	$57.27	$57.25	$57.30
Purchase #3	$239.33	13.535%	$271.7233	$271.72	$271.70	$271.70
Purchase #4	$120.75	10.802%	$133.7934	$133.79	$133.80	$133.80
Purchase #5	$7.46	5.750%	$7.889	$7.89	$7.90	$7.90
Purchase #6	$31.91	11.840%	$35.6881	$35.69	$35.70	$35.70
Purchase #7	$87.40	3.800%	$90.7212	$90.72	$90.70	$90.70
7 purchase totals =	$619.62		$687.7520	$687.74	$687.70	$687.80