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	$6.70	8.851%	$7.293	$7.29	$7.30	$7.30
Purchase #2	$132.74	7.869%	$143.1853	$143.19	$143.20	$143.20
Purchase #3	$239.67	10.369%	$264.5214	$264.52	$264.50	$264.50
Purchase #4	$210.94	5.215%	$221.9405	$221.94	$221.95	$221.90
Purchase #5	$100.61	8.527%	$109.189	$109.19	$109.20	$109.20
Purchase #6	$69.35	6.221%	$73.6643	$73.66	$73.65	$73.70
Purchase #7	$243.38	7.781%	$262.3174	$262.32	$262.30	$262.30
7 purchase totals =	$1,003.39		$1,082.1109	$1,082.11	$1,082.10	$1,082.10