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	$42.37	6.868%	$45.28	$45.28	$45.30	$45.30
Purchase #2	$131.68	9.525%	$144.2225	$144.22	$144.20	$144.20
Purchase #3	$28.92	8.803%	$31.4658	$31.47	$31.45	$31.50
Purchase #4	$134.84	13.356%	$152.8492	$152.85	$152.85	$152.80
Purchase #5	$67.63	11.716%	$75.5535	$75.55	$75.55	$75.60
Purchase #6	$159.69	5.824%	$168.9903	$168.99	$169.00	$169.00
Purchase #7	$37.97	11.865%	$42.4751	$42.48	$42.50	$42.50
7 purchase totals =	$603.10		$660.8364	$660.84	$660.85	$660.90