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	$153.78	3.515%	$159.1854	$159.19	$159.20	$159.20
Purchase #2	$123.67	12.788%	$139.4849	$139.48	$139.50	$139.50
Purchase #3	$68.33	6.585%	$72.8295	$72.83	$72.85	$72.80
Purchase #4	$190.95	8.296%	$206.7912	$206.79	$206.80	$206.80
Purchase #5	$81.33	4.659%	$85.1192	$85.12	$85.10	$85.10
Purchase #6	$89.52	8.695%	$97.3038	$97.30	$97.30	$97.30
Purchase #7	$135.60	12.681%	$152.7954	$152.80	$152.80	$152.80
7 purchase totals =	$843.18		$913.5094	$913.51	$913.55	$913.50