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	$136.47	4.270%	$142.2973	$142.30	$142.30	$142.30
Purchase #2	$86.91	3.680%	$90.1083	$90.11	$90.10	$90.10
Purchase #3	$146.61	9.126%	$159.9896	$159.99	$160.00	$160.00
Purchase #4	$228.33	4.157%	$237.8217	$237.82	$237.80	$237.80
Purchase #5	$175.40	5.374%	$184.826	$184.83	$184.85	$184.80
Purchase #6	$90.85	13.856%	$103.4382	$103.44	$103.45	$103.40
Purchase #7	$80.92	13.678%	$91.9882	$91.99	$92.00	$92.00
7 purchase totals =	$945.49		$1,010.4693	$1,010.48	$1,010.50	$1,010.40