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	$29.55	8.150%	$31.9583	$31.96	$31.95	$32.00
Purchase #2	$178.44	10.201%	$196.6427	$196.64	$196.65	$196.60
Purchase #3	$78.36	8.609%	$85.106	$85.11	$85.10	$85.10
Purchase #4	$82.78	8.809%	$90.0721	$90.07	$90.05	$90.10
Purchase #5	$212.68	4.170%	$221.5488	$221.55	$221.55	$221.50
Purchase #6	$173.56	3.296%	$179.2805	$179.28	$179.30	$179.30
Purchase #7	$61.95	7.428%	$66.5516	$66.55	$66.55	$66.60
7 purchase totals =	$817.32		$871.1600	$871.16	$871.15	$871.20