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	$33.36	11.289%	$37.126	$37.13	$37.15	$37.10
Purchase #2	$234.33	6.391%	$249.306	$249.31	$249.30	$249.30
Purchase #3	$210.53	6.232%	$223.6502	$223.65	$223.65	$223.70
Purchase #4	$107.33	10.309%	$118.3946	$118.39	$118.40	$118.40
Purchase #5	$234.80	5.249%	$247.1247	$247.12	$247.10	$247.10
Purchase #6	$161.38	7.599%	$173.6433	$173.64	$173.65	$173.60
Purchase #7	$84.80	6.610%	$90.4053	$90.41	$90.40	$90.40
7 purchase totals =	$1,066.53		$1,139.6501	$1,139.65	$1,139.65	$1,139.60