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	$32.93	13.861%	$37.4944	$37.49	$37.50	$37.50
Purchase #2	$24.35	10.445%	$26.8934	$26.89	$26.90	$26.90
Purchase #3	$166.99	12.843%	$188.4365	$188.44	$188.45	$188.40
Purchase #4	$37.27	13.160%	$42.1747	$42.17	$42.15	$42.20
Purchase #5	$39.48	4.458%	$41.24	$41.24	$41.25	$41.20
Purchase #6	$16.53	10.759%	$18.3085	$18.31	$18.30	$18.30
Purchase #7	$91.86	5.662%	$97.0611	$97.06	$97.05	$97.10
7 purchase totals =	$409.41		$451.6086	$451.60	$451.60	$451.60