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	$7.40	3.760%	$7.6782	$7.68	$7.70	$7.70
Purchase #2	$88.68	12.820%	$100.0488	$100.05	$100.05	$100.00
Purchase #3	$33.91	11.746%	$37.8931	$37.89	$37.90	$37.90
Purchase #4	$189.71	9.710%	$208.1308	$208.13	$208.15	$208.10
Purchase #5	$112.55	9.857%	$123.6441	$123.64	$123.65	$123.60
Purchase #6	$173.93	7.836%	$187.5592	$187.56	$187.55	$187.60
Purchase #7	$193.38	8.188%	$209.214	$209.21	$209.20	$209.20
7 purchase totals =	$799.56		$874.1682	$874.16	$874.20	$874.10