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	$18.60	11.258%	$20.694	$20.69	$20.70	$20.70
Purchase #2	$215.74	7.316%	$231.5235	$231.52	$231.50	$231.50
Purchase #3	$130.82	7.302%	$140.3725	$140.37	$140.35	$140.40
Purchase #4	$80.60	12.532%	$90.7008	$90.70	$90.70	$90.70
Purchase #5	$212.53	3.459%	$219.8814	$219.88	$219.90	$219.90
Purchase #6	$171.88	12.452%	$193.2825	$193.28	$193.30	$193.30
Purchase #7	$175.93	11.821%	$196.7267	$196.73	$196.75	$196.70
7 purchase totals =	$1,006.10		$1,093.1814	$1,093.17	$1,093.20	$1,093.20