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	$39.54	6.112%	$41.9567	$41.96	$41.95	$42.00
Purchase #2	$205.89	10.459%	$227.424	$227.42	$227.40	$227.40
Purchase #3	$205.37	5.335%	$216.3265	$216.33	$216.35	$216.30
Purchase #4	$136.64	4.557%	$142.8667	$142.87	$142.85	$142.90
Purchase #5	$57.64	4.371%	$60.1594	$60.16	$60.15	$60.20
Purchase #6	$200.84	13.820%	$228.5961	$228.60	$228.60	$228.60
Purchase #7	$216.99	7.610%	$233.5029	$233.50	$233.50	$233.50
7 purchase totals =	$1,062.91		$1,150.8323	$1,150.84	$1,150.80	$1,150.90