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	$28.31	11.448%	$31.5509	$31.55	$31.55	$31.60
Purchase #2	$118.36	4.155%	$123.2779	$123.28	$123.30	$123.30
Purchase #3	$36.39	8.724%	$39.5647	$39.56	$39.55	$39.60
Purchase #4	$5.48	13.321%	$6.21	$6.21	$6.20	$6.20
Purchase #5	$217.51	5.665%	$229.8319	$229.83	$229.85	$229.80
Purchase #6	$156.62	7.466%	$168.3132	$168.31	$168.30	$168.30
Purchase #7	$73.70	10.405%	$81.3685	$81.37	$81.35	$81.40
7 purchase totals =	$636.37		$680.1171	$680.11	$680.10	$680.20