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	$59.89	12.603%	$67.4379	$67.44	$67.45	$67.40
Purchase #2	$28.33	10.660%	$31.35	$31.35	$31.35	$31.40
Purchase #3	$108.26	7.787%	$116.6902	$116.69	$116.70	$116.70
Purchase #4	$101.66	8.449%	$110.2493	$110.25	$110.25	$110.20
Purchase #5	$38.75	9.705%	$42.5107	$42.51	$42.50	$42.50
Purchase #6	$65.33	10.222%	$72.008	$72.01	$72.00	$72.00
Purchase #7	$61.56	4.673%	$64.4367	$64.44	$64.45	$64.40
7 purchase totals =	$463.78		$504.6828	$504.69	$504.70	$504.60