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	$138.89	5.202%	$146.1151	$146.12	$146.10	$146.10
Purchase #2	$224.63	13.621%	$255.2269	$255.23	$255.25	$255.20
Purchase #3	$220.57	12.380%	$247.8766	$247.88	$247.90	$247.90
Purchase #4	$116.80	12.711%	$131.6464	$131.65	$131.65	$131.60
Purchase #5	$62.72	13.444%	$71.1521	$71.15	$71.15	$71.20
Purchase #6	$76.72	9.190%	$83.7706	$83.77	$83.75	$83.80
Purchase #7	$89.83	4.285%	$93.6792	$93.68	$93.70	$93.70
7 purchase totals =	$930.16		$1,029.4669	$1,029.48	$1,029.50	$1,029.50