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	$18.31	11.716%	$20.4552	$20.46	$20.45	$20.50
Purchase #2	$237.41	13.737%	$270.023	$270.02	$270.00	$270.00
Purchase #3	$132.51	6.317%	$140.8807	$140.88	$140.90	$140.90
Purchase #4	$64.83	10.133%	$71.3992	$71.40	$71.40	$71.40
Purchase #5	$162.40	8.192%	$175.7038	$175.70	$175.70	$175.70
Purchase #6	$40.53	11.722%	$45.2809	$45.28	$45.30	$45.30
Purchase #7	$197.56	12.434%	$222.1246	$222.12	$222.10	$222.10
7 purchase totals =	$853.55		$945.8674	$945.86	$945.85	$945.90