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	$101.36	10.412%	$111.9136	$111.91	$111.90	$111.90
Purchase #2	$238.82	11.784%	$266.9625	$266.96	$266.95	$267.00
Purchase #3	$20.41	6.829%	$21.8038	$21.80	$21.80	$21.80
Purchase #4	$233.76	4.182%	$243.5358	$243.54	$243.55	$243.50
Purchase #5	$249.96	12.709%	$281.7274	$281.73	$281.75	$281.70
Purchase #6	$35.89	4.275%	$37.4243	$37.42	$37.40	$37.40
Purchase #7	$76.92	3.822%	$79.8599	$79.86	$79.85	$79.90
7 purchase totals =	$957.12		$1,043.2273	$1,043.22	$1,043.20	$1,043.20