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	$32.54	11.714%	$36.3517	$36.35	$36.35	$36.40
Purchase #2	$181.94	4.443%	$190.0236	$190.02	$190.00	$190.00
Purchase #3	$50.60	8.379%	$54.8398	$54.84	$54.85	$54.80
Purchase #4	$123.41	6.424%	$131.3379	$131.34	$131.35	$131.30
Purchase #5	$24.35	12.572%	$27.4113	$27.41	$27.40	$27.40
Purchase #6	$53.32	7.765%	$57.4603	$57.46	$57.45	$57.50
Purchase #7	$215.51	7.454%	$231.5741	$231.57	$231.55	$231.60
7 purchase totals =	$681.67		$728.9987	$728.99	$728.95	$729.00