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	$28.40	13.370%	$32.1971	$32.20	$32.20	$32.20
Purchase #2	$231.87	7.577%	$249.4388	$249.44	$249.45	$249.40
Purchase #3	$189.66	3.316%	$195.9491	$195.95	$195.95	$195.90
Purchase #4	$79.29	6.398%	$84.363	$84.36	$84.35	$84.40
Purchase #5	$165.40	4.292%	$172.499	$172.50	$172.50	$172.50
Purchase #6	$102.84	8.517%	$111.5989	$111.60	$111.60	$111.60
Purchase #7	$82.82	9.663%	$90.8229	$90.82	$90.80	$90.80
7 purchase totals =	$880.28		$936.8688	$936.87	$936.85	$936.80