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	$131.52	11.609%	$146.7882	$146.79	$146.80	$146.80
Purchase #2	$24.99	9.313%	$27.3173	$27.32	$27.30	$27.30
Purchase #3	$53.91	10.526%	$59.5846	$59.58	$59.60	$59.60
Purchase #4	$55.99	9.626%	$61.3796	$61.38	$61.40	$61.40
Purchase #5	$54.25	12.174%	$60.8544	$60.85	$60.85	$60.90
Purchase #6	$95.64	10.412%	$105.598	$105.60	$105.60	$105.60
Purchase #7	$38.38	7.759%	$41.3579	$41.36	$41.35	$41.40
7 purchase totals =	$454.68		$502.8800	$502.88	$502.90	$503.00