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	$28.62	12.184%	$32.1071	$32.11	$32.10	$32.10
Purchase #2	$111.29	12.874%	$125.6175	$125.62	$125.60	$125.60
Purchase #3	$103.41	8.170%	$111.8586	$111.86	$111.85	$111.90
Purchase #4	$49.98	6.783%	$53.3701	$53.37	$53.35	$53.40
Purchase #5	$129.30	10.471%	$142.839	$142.84	$142.85	$142.80
Purchase #6	$225.76	5.160%	$237.4092	$237.41	$237.40	$237.40
Purchase #7	$203.50	9.621%	$223.0787	$223.08	$223.10	$223.10
7 purchase totals =	$851.86		$926.2802	$926.29	$926.25	$926.30