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	$24.64	9.429%	$26.9633	$26.96	$26.95	$27.00
Purchase #2	$165.89	5.795%	$175.5033	$175.50	$175.50	$175.50
Purchase #3	$108.83	3.574%	$112.7196	$112.72	$112.70	$112.70
Purchase #4	$80.89	11.146%	$89.906	$89.91	$89.90	$89.90
Purchase #5	$88.66	3.654%	$91.8996	$91.90	$91.90	$91.90
Purchase #6	$119.31	11.608%	$133.1595	$133.16	$133.15	$133.20
Purchase #7	$69.54	4.754%	$72.8459	$72.85	$72.85	$72.80
7 purchase totals =	$657.76		$702.9972	$703.00	$702.95	$703.00