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	$212.91	4.496%	$222.4824	$222.48	$222.50	$222.50
Purchase #2	$100.91	3.140%	$104.0786	$104.08	$104.10	$104.10
Purchase #3	$246.32	5.524%	$259.9267	$259.93	$259.95	$259.90
Purchase #4	$80.29	11.139%	$89.2335	$89.23	$89.25	$89.20
Purchase #5	$80.89	9.234%	$88.3594	$88.36	$88.35	$88.40
Purchase #6	$158.39	12.306%	$177.8815	$177.88	$177.90	$177.90
Purchase #7	$73.28	6.396%	$77.967	$77.97	$77.95	$78.00
7 purchase totals =	$952.99		$1,019.9291	$1,019.93	$1,020.00	$1,020.00