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	$170.55	3.729%	$176.9098	$176.91	$176.90	$176.90
Purchase #2	$96.47	11.379%	$107.4473	$107.45	$107.45	$107.40
Purchase #3	$110.82	11.330%	$123.3759	$123.38	$123.40	$123.40
Purchase #4	$19.27	6.398%	$20.5029	$20.50	$20.50	$20.50
Purchase #5	$150.41	12.816%	$169.6865	$169.69	$169.70	$169.70
Purchase #6	$87.37	3.483%	$90.4131	$90.41	$90.40	$90.40
Purchase #7	$60.58	10.262%	$66.7967	$66.80	$66.80	$66.80
7 purchase totals =	$695.47		$755.1322	$755.14	$755.15	$755.10