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	$102.37	6.524%	$109.0486	$109.05	$109.05	$109.00
Purchase #2	$222.49	6.786%	$237.5882	$237.59	$237.60	$237.60
Purchase #3	$148.69	11.211%	$165.3596	$165.36	$165.35	$165.40
Purchase #4	$113.45	4.142%	$118.1491	$118.15	$118.15	$118.10
Purchase #5	$233.77	6.624%	$249.2549	$249.25	$249.25	$249.30
Purchase #6	$246.97	13.568%	$280.4789	$280.48	$280.50	$280.50
Purchase #7	$20.31	6.782%	$21.6874	$21.69	$21.70	$21.70
7 purchase totals =	$1,088.05		$1,181.5667	$1,181.57	$1,181.60	$1,181.60