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	$10.76	12.502%	$12.1052	$12.11	$12.10	$12.10
Purchase #2	$190.96	9.222%	$208.5703	$208.57	$208.55	$208.60
Purchase #3	$133.58	13.230%	$151.2526	$151.25	$151.25	$151.30
Purchase #4	$224.28	13.628%	$254.8449	$254.84	$254.85	$254.80
Purchase #5	$29.32	4.172%	$30.5432	$30.54	$30.55	$30.50
Purchase #6	$119.29	10.618%	$131.9562	$131.96	$131.95	$132.00
Purchase #7	$238.54	10.780%	$264.2546	$264.25	$264.25	$264.30
7 purchase totals =	$946.73		$1,053.5270	$1,053.52	$1,053.50	$1,053.60