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	$206.94	11.844%	$231.45	$231.45	$231.45	$231.50
Purchase #2	$123.86	5.746%	$130.977	$130.98	$131.00	$131.00
Purchase #3	$208.98	6.417%	$222.3902	$222.39	$222.40	$222.40
Purchase #4	$87.98	13.784%	$100.1072	$100.11	$100.10	$100.10
Purchase #5	$88.34	5.769%	$93.4363	$93.44	$93.45	$93.40
Purchase #6	$237.56	3.519%	$245.9197	$245.92	$245.90	$245.90
Purchase #7	$132.41	4.560%	$138.4479	$138.45	$138.45	$138.40
7 purchase totals =	$1,086.07		$1,162.7283	$1,162.74	$1,162.75	$1,162.70