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	$28.54	12.257%	$32.0381	$32.04	$32.05	$32.00
Purchase #2	$217.52	12.793%	$245.3473	$245.35	$245.35	$245.30
Purchase #3	$38.45	9.215%	$41.9932	$41.99	$42.00	$42.00
Purchase #4	$152.81	9.578%	$167.4461	$167.45	$167.45	$167.40
Purchase #5	$87.32	4.370%	$91.1359	$91.14	$91.15	$91.10
Purchase #6	$64.29	11.294%	$71.5509	$71.55	$71.55	$71.60
Purchase #7	$20.54	6.403%	$21.8552	$21.86	$21.85	$21.90
7 purchase totals =	$609.47		$671.3667	$671.38	$671.40	$671.30