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	$67.29	13.734%	$76.5316	$76.53	$76.55	$76.50
Purchase #2	$39.40	5.630%	$41.6182	$41.62	$41.60	$41.60
Purchase #3	$136.50	8.474%	$148.067	$148.07	$148.05	$148.10
Purchase #4	$31.59	11.113%	$35.1006	$35.10	$35.10	$35.10
Purchase #5	$72.52	8.123%	$78.4108	$78.41	$78.40	$78.40
Purchase #6	$236.91	8.529%	$257.1161	$257.12	$257.10	$257.10
Purchase #7	$117.72	10.493%	$130.0724	$130.07	$130.05	$130.10
7 purchase totals =	$701.93		$766.9167	$766.92	$766.85	$766.90