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	$124.33	9.656%	$136.3353	$136.34	$136.35	$136.30
Purchase #2	$43.51	13.688%	$49.4656	$49.47	$49.45	$49.50
Purchase #3	$247.47	10.382%	$273.1623	$273.16	$273.15	$273.20
Purchase #4	$189.30	3.568%	$196.0542	$196.05	$196.05	$196.10
Purchase #5	$5.28	9.499%	$5.7815	$5.78	$5.80	$5.80
Purchase #6	$82.51	7.755%	$88.9087	$88.91	$88.90	$88.90
Purchase #7	$54.95	4.659%	$57.5101	$57.51	$57.50	$57.50
7 purchase totals =	$747.35		$807.2177	$807.22	$807.20	$807.30