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	$30.69	8.772%	$33.3821	$33.38	$33.40	$33.40
Purchase #2	$225.66	13.417%	$255.9368	$255.94	$255.95	$255.90
Purchase #3	$90.85	6.134%	$96.4227	$96.42	$96.40	$96.40
Purchase #4	$225.99	8.788%	$245.85	$245.85	$245.85	$245.90
Purchase #5	$128.29	7.676%	$138.1375	$138.14	$138.15	$138.10
Purchase #6	$132.85	6.384%	$141.3311	$141.33	$141.35	$141.30
Purchase #7	$214.73	4.251%	$223.8582	$223.86	$223.85	$223.90
7 purchase totals =	$1,049.06		$1,134.9184	$1,134.92	$1,134.95	$1,134.90