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	$147.72	8.229%	$159.8759	$159.88	$159.90	$159.90
Purchase #2	$159.31	6.378%	$169.4708	$169.47	$169.45	$169.50
Purchase #3	$73.91	13.356%	$83.7814	$83.78	$83.80	$83.80
Purchase #4	$159.30	12.455%	$179.1408	$179.14	$179.15	$179.10
Purchase #5	$144.73	5.508%	$152.7017	$152.70	$152.70	$152.70
Purchase #6	$55.73	6.734%	$59.4829	$59.48	$59.50	$59.50
Purchase #7	$18.56	9.120%	$20.2527	$20.25	$20.25	$20.30
7 purchase totals =	$759.26		$824.7062	$824.70	$824.75	$824.80