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	$155.95	5.172%	$164.0157	$164.02	$164.00	$164.00
Purchase #2	$84.61	5.713%	$89.4438	$89.44	$89.45	$89.40
Purchase #3	$160.82	13.203%	$182.0531	$182.05	$182.05	$182.10
Purchase #4	$15.50	9.494%	$16.9716	$16.97	$16.95	$17.00
Purchase #5	$128.39	9.319%	$140.3547	$140.35	$140.35	$140.40
Purchase #6	$132.73	13.110%	$150.1309	$150.13	$150.15	$150.10
Purchase #7	$42.31	3.455%	$43.7718	$43.77	$43.75	$43.80
7 purchase totals =	$720.31		$786.7416	$786.73	$786.70	$786.80