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	$29.98	3.737%	$31.1004	$31.10	$31.10	$31.10
Purchase #2	$213.72	13.344%	$242.2388	$242.24	$242.25	$242.20
Purchase #3	$221.33	7.165%	$237.1883	$237.19	$237.20	$237.20
Purchase #4	$125.31	12.311%	$140.7369	$140.74	$140.75	$140.70
Purchase #5	$188.56	10.772%	$208.8717	$208.87	$208.85	$208.90
Purchase #6	$10.82	7.380%	$11.6185	$11.62	$11.60	$11.60
Purchase #7	$124.26	6.111%	$131.8535	$131.85	$131.85	$131.90
7 purchase totals =	$913.98		$1,003.6081	$1,003.61	$1,003.60	$1,003.60