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	$64.81	12.491%	$72.9054	$72.91	$72.90	$72.90
Purchase #2	$173.93	6.304%	$184.8945	$184.89	$184.90	$184.90
Purchase #3	$182.68	3.571%	$189.2035	$189.20	$189.20	$189.20
Purchase #4	$6.57	9.863%	$7.218	$7.22	$7.20	$7.20
Purchase #5	$83.63	6.771%	$89.2926	$89.29	$89.30	$89.30
Purchase #6	$180.81	9.761%	$198.4589	$198.46	$198.45	$198.50
Purchase #7	$174.82	7.404%	$187.7637	$187.76	$187.75	$187.80
7 purchase totals =	$867.25		$929.7366	$929.73	$929.70	$929.80