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	$138.61	11.234%	$154.1814	$154.18	$154.20	$154.20
Purchase #2	$235.25	13.641%	$267.3405	$267.34	$267.35	$267.30
Purchase #3	$82.89	7.657%	$89.2369	$89.24	$89.25	$89.20
Purchase #4	$175.99	4.556%	$184.0081	$184.01	$184.00	$184.00
Purchase #5	$104.91	6.237%	$111.4532	$111.45	$111.45	$111.50
Purchase #6	$212.71	7.439%	$228.5335	$228.53	$228.55	$228.50
Purchase #7	$161.41	12.769%	$182.0204	$182.02	$182.00	$182.00
7 purchase totals =	$1,111.77		$1,216.7740	$1,216.77	$1,216.80	$1,216.70