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	$180.51	5.195%	$189.8875	$189.89	$189.90	$189.90
Purchase #2	$45.71	3.850%	$47.4698	$47.47	$47.45	$47.50
Purchase #3	$188.89	4.590%	$197.5601	$197.56	$197.55	$197.60
Purchase #4	$109.47	6.268%	$116.3316	$116.33	$116.35	$116.30
Purchase #5	$177.55	7.105%	$190.1649	$190.16	$190.15	$190.20
Purchase #6	$204.36	7.628%	$219.9486	$219.95	$219.95	$219.90
Purchase #7	$205.85	6.144%	$218.4974	$218.50	$218.50	$218.50
7 purchase totals =	$1,112.34		$1,179.8599	$1,179.86	$1,179.85	$1,179.90