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	$180.45	5.806%	$190.9269	$190.93	$190.95	$190.90
Purchase #2	$42.36	3.504%	$43.8443	$43.84	$43.85	$43.80
Purchase #3	$71.94	12.474%	$80.9138	$80.91	$80.90	$80.90
Purchase #4	$148.89	5.295%	$156.7737	$156.77	$156.75	$156.80
Purchase #5	$232.66	11.151%	$258.6039	$258.60	$258.60	$258.60
Purchase #6	$58.95	5.110%	$61.9623	$61.96	$61.95	$62.00
Purchase #7	$155.39	11.432%	$173.1542	$173.15	$173.15	$173.20
7 purchase totals =	$890.64		$966.1791	$966.16	$966.15	$966.20