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	$244.77	5.540%	$258.3303	$258.33	$258.35	$258.30
Purchase #2	$154.26	9.226%	$168.492	$168.49	$168.50	$168.50
Purchase #3	$173.59	6.842%	$185.467	$185.47	$185.45	$185.50
Purchase #4	$71.75	9.871%	$78.8324	$78.83	$78.85	$78.80
Purchase #5	$232.93	13.343%	$264.0098	$264.01	$264.00	$264.00
Purchase #6	$227.93	8.529%	$247.3701	$247.37	$247.35	$247.40
Purchase #7	$65.44	12.659%	$73.724	$73.72	$73.70	$73.70
7 purchase totals =	$1,170.67		$1,276.2256	$1,276.22	$1,276.20	$1,276.20