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	$91.28	10.311%	$100.6919	$100.69	$100.70	$100.70
Purchase #2	$76.34	13.189%	$86.4085	$86.41	$86.40	$86.40
Purchase #3	$181.34	12.759%	$204.4772	$204.48	$204.50	$204.50
Purchase #4	$127.60	5.474%	$134.5848	$134.58	$134.60	$134.60
Purchase #5	$118.62	5.782%	$125.4786	$125.48	$125.50	$125.50
Purchase #6	$178.32	6.512%	$189.9322	$189.93	$189.95	$189.90
Purchase #7	$43.42	5.707%	$45.898	$45.90	$45.90	$45.90
7 purchase totals =	$816.92		$887.4712	$887.47	$887.55	$887.50