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	$16.49	10.307%	$18.1896	$18.19	$18.20	$18.20
Purchase #2	$56.36	10.807%	$62.4508	$62.45	$62.45	$62.50
Purchase #3	$100.54	3.845%	$104.4058	$104.41	$104.40	$104.40
Purchase #4	$241.98	7.260%	$259.5477	$259.55	$259.55	$259.50
Purchase #5	$108.85	3.707%	$112.8851	$112.89	$112.90	$112.90
Purchase #6	$245.46	11.292%	$273.1773	$273.18	$273.20	$273.20
Purchase #7	$236.26	11.829%	$264.2072	$264.21	$264.20	$264.20
7 purchase totals =	$1,005.94		$1,094.8635	$1,094.88	$1,094.90	$1,094.90