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	$37.67	12.137%	$42.242	$42.24	$42.25	$42.20
Purchase #2	$165.97	6.330%	$176.4759	$176.48	$176.50	$176.50
Purchase #3	$246.82	3.499%	$255.4562	$255.46	$255.45	$255.50
Purchase #4	$130.50	13.375%	$147.9544	$147.95	$147.95	$148.00
Purchase #5	$102.81	12.716%	$115.8833	$115.88	$115.90	$115.90
Purchase #6	$53.94	13.595%	$61.2731	$61.27	$61.25	$61.30
Purchase #7	$208.94	11.828%	$233.6534	$233.65	$233.65	$233.70
7 purchase totals =	$946.65		$1,032.9383	$1,032.93	$1,032.95	$1,033.10