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	$134.74	9.502%	$147.543	$147.54	$147.55	$147.50
Purchase #2	$173.66	13.256%	$196.6804	$196.68	$196.70	$196.70
Purchase #3	$49.83	11.479%	$55.55	$55.55	$55.55	$55.60
Purchase #4	$137.62	3.482%	$142.4119	$142.41	$142.40	$142.40
Purchase #5	$26.47	3.833%	$27.4846	$27.48	$27.50	$27.50
Purchase #6	$192.52	12.524%	$216.6312	$216.63	$216.65	$216.60
Purchase #7	$42.48	13.778%	$48.3329	$48.33	$48.35	$48.30
7 purchase totals =	$757.32		$834.6340	$834.62	$834.70	$834.60