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	$180.35	4.772%	$188.9563	$188.96	$188.95	$189.00
Purchase #2	$89.77	3.167%	$92.613	$92.61	$92.60	$92.60
Purchase #3	$81.41	9.326%	$89.0023	$89.00	$89.00	$89.00
Purchase #4	$96.54	13.481%	$109.5546	$109.55	$109.55	$109.60
Purchase #5	$45.91	11.303%	$51.0992	$51.10	$51.10	$51.10
Purchase #6	$29.85	7.696%	$32.1473	$32.15	$32.15	$32.10
Purchase #7	$206.51	9.666%	$226.4713	$226.47	$226.45	$226.50
7 purchase totals =	$730.34		$789.8440	$789.84	$789.80	$789.90