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	$246.34	12.710%	$277.6498	$277.65	$277.65	$277.60
Purchase #2	$164.56	12.350%	$184.8832	$184.88	$184.90	$184.90
Purchase #3	$50.44	13.832%	$57.4169	$57.42	$57.40	$57.40
Purchase #4	$237.77	5.306%	$250.3861	$250.39	$250.40	$250.40
Purchase #5	$35.67	12.716%	$40.2058	$40.21	$40.20	$40.20
Purchase #6	$29.80	11.147%	$33.1218	$33.12	$33.10	$33.10
Purchase #7	$229.25	8.142%	$247.9155	$247.92	$247.90	$247.90
7 purchase totals =	$993.83		$1,091.5791	$1,091.59	$1,091.55	$1,091.50