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	$164.97	11.758%	$184.3672	$184.37	$184.35	$184.40
Purchase #2	$12.63	5.388%	$13.3105	$13.31	$13.30	$13.30
Purchase #3	$189.94	4.301%	$198.1093	$198.11	$198.10	$198.10
Purchase #4	$104.58	6.706%	$111.5931	$111.59	$111.60	$111.60
Purchase #5	$72.48	11.175%	$80.5796	$80.58	$80.60	$80.60
Purchase #6	$160.43	12.551%	$180.5656	$180.57	$180.55	$180.60
Purchase #7	$79.67	7.539%	$85.6763	$85.68	$85.70	$85.70
7 purchase totals =	$784.70		$854.2016	$854.21	$854.20	$854.30