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	$165.52	11.692%	$184.8726	$184.87	$184.85	$184.90
Purchase #2	$63.85	12.677%	$71.9443	$71.94	$71.95	$71.90
Purchase #3	$22.43	8.600%	$24.359	$24.36	$24.35	$24.40
Purchase #4	$170.25	5.665%	$179.8947	$179.89	$179.90	$179.90
Purchase #5	$133.34	4.761%	$139.6883	$139.69	$139.70	$139.70
Purchase #6	$136.97	10.192%	$150.93	$150.93	$150.95	$150.90
Purchase #7	$156.54	3.611%	$162.1927	$162.19	$162.20	$162.20
7 purchase totals =	$848.90		$913.8816	$913.87	$913.90	$913.90