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	$19.25	10.753%	$21.32	$21.32	$21.30	$21.30
Purchase #2	$213.63	8.816%	$232.4636	$232.46	$232.45	$232.50
Purchase #3	$247.90	5.764%	$262.189	$262.19	$262.20	$262.20
Purchase #4	$184.81	10.464%	$204.1485	$204.15	$204.15	$204.10
Purchase #5	$86.58	10.741%	$95.8796	$95.88	$95.90	$95.90
Purchase #6	$101.69	9.780%	$111.6353	$111.64	$111.65	$111.60
Purchase #7	$37.30	9.124%	$40.7033	$40.70	$40.70	$40.70
7 purchase totals =	$891.16		$968.3393	$968.34	$968.35	$968.30