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	$129.69	8.337%	$140.5023	$140.50	$140.50	$140.50
Purchase #2	$159.49	13.415%	$180.8856	$180.89	$180.90	$180.90
Purchase #3	$133.67	7.824%	$144.1283	$144.13	$144.15	$144.10
Purchase #4	$58.94	4.196%	$61.4131	$61.41	$61.40	$61.40
Purchase #5	$126.38	12.276%	$141.8944	$141.89	$141.90	$141.90
Purchase #6	$131.32	8.533%	$142.5255	$142.53	$142.55	$142.50
Purchase #7	$245.30	5.797%	$259.52	$259.52	$259.50	$259.50
7 purchase totals =	$984.79		$1,070.8692	$1,070.87	$1,070.90	$1,070.80