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	$6.45	12.235%	$7.2392	$7.24	$7.25	$7.20
Purchase #2	$36.69	6.126%	$38.9376	$38.94	$38.95	$38.90
Purchase #3	$124.54	4.736%	$130.4382	$130.44	$130.45	$130.40
Purchase #4	$55.56	10.140%	$61.1938	$61.19	$61.20	$61.20
Purchase #5	$76.59	3.261%	$79.0876	$79.09	$79.10	$79.10
Purchase #6	$85.44	6.362%	$90.8757	$90.88	$90.90	$90.90
Purchase #7	$97.38	13.611%	$110.6344	$110.63	$110.65	$110.60
7 purchase totals =	$482.65		$518.4065	$518.41	$518.50	$518.30