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	$242.65	3.535%	$251.2277	$251.23	$251.25	$251.20
Purchase #2	$62.56	8.518%	$67.8889	$67.89	$67.90	$67.90
Purchase #3	$197.40	6.302%	$209.8401	$209.84	$209.85	$209.80
Purchase #4	$115.34	10.659%	$127.6341	$127.63	$127.65	$127.60
Purchase #5	$109.98	8.601%	$119.4394	$119.44	$119.45	$119.40
Purchase #6	$160.80	13.571%	$182.6222	$182.62	$182.60	$182.60
Purchase #7	$41.44	9.765%	$45.4866	$45.49	$45.50	$45.50
7 purchase totals =	$930.17		$1,004.1390	$1,004.14	$1,004.20	$1,004.00