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	$210.85	3.720%	$218.6936	$218.69	$218.70	$218.70
Purchase #2	$92.33	6.464%	$98.2982	$98.30	$98.30	$98.30
Purchase #3	$45.36	8.189%	$49.0745	$49.07	$49.05	$49.10
Purchase #4	$142.88	10.816%	$158.3339	$158.33	$158.35	$158.30
Purchase #5	$102.41	7.141%	$109.7231	$109.72	$109.70	$109.70
Purchase #6	$232.88	13.693%	$264.7683	$264.77	$264.75	$264.80
Purchase #7	$99.31	4.850%	$104.1265	$104.13	$104.15	$104.10
7 purchase totals =	$926.02		$1,003.0181	$1,003.01	$1,003.00	$1,003.00