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	$31.75	5.628%	$33.5369	$33.54	$33.55	$33.50
Purchase #2	$161.87	12.459%	$182.0374	$182.04	$182.05	$182.00
Purchase #3	$161.84	7.612%	$174.1593	$174.16	$174.15	$174.20
Purchase #4	$225.44	10.578%	$249.287	$249.29	$249.30	$249.30
Purchase #5	$143.69	5.519%	$151.6203	$151.62	$151.60	$151.60
Purchase #6	$72.61	13.141%	$82.1517	$82.15	$82.15	$82.20
Purchase #7	$212.30	5.208%	$223.3566	$223.36	$223.35	$223.40
7 purchase totals =	$1,009.50		$1,096.1492	$1,096.16	$1,096.15	$1,096.20