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	$128.60	4.529%	$134.4243	$134.42	$134.40	$134.40
Purchase #2	$56.38	5.317%	$59.3777	$59.38	$59.40	$59.40
Purchase #3	$35.31	12.241%	$39.6323	$39.63	$39.65	$39.60
Purchase #4	$209.59	7.126%	$224.5254	$224.53	$224.55	$224.50
Purchase #5	$236.99	5.647%	$250.3728	$250.37	$250.35	$250.40
Purchase #6	$58.76	9.168%	$64.1471	$64.15	$64.15	$64.10
Purchase #7	$150.69	13.383%	$170.8568	$170.86	$170.85	$170.90
7 purchase totals =	$876.32		$943.3364	$943.34	$943.35	$943.30