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	$96.29	3.254%	$99.4233	$99.42	$99.40	$99.40
Purchase #2	$163.89	10.801%	$181.5918	$181.59	$181.60	$181.60
Purchase #3	$128.84	3.410%	$133.2334	$133.23	$133.25	$133.20
Purchase #4	$197.78	9.715%	$216.9943	$216.99	$217.00	$217.00
Purchase #5	$250.54	11.122%	$278.4051	$278.41	$278.40	$278.40
Purchase #6	$36.73	9.261%	$40.1316	$40.13	$40.15	$40.10
Purchase #7	$54.66	9.167%	$59.6707	$59.67	$59.65	$59.70
7 purchase totals =	$928.73		$1,009.4502	$1,009.44	$1,009.45	$1,009.40