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	$30.33	11.736%	$33.8895	$33.89	$33.90	$33.90
Purchase #2	$109.56	7.270%	$117.525	$117.53	$117.55	$117.50
Purchase #3	$250.48	13.269%	$283.7162	$283.72	$283.70	$283.70
Purchase #4	$103.87	4.546%	$108.5919	$108.59	$108.60	$108.60
Purchase #5	$113.77	11.813%	$127.2097	$127.21	$127.20	$127.20
Purchase #6	$227.66	5.160%	$239.4073	$239.41	$239.40	$239.40
Purchase #7	$164.79	9.627%	$180.6543	$180.65	$180.65	$180.70
7 purchase totals =	$1,000.46		$1,090.9939	$1,091.00	$1,091.00	$1,091.00