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	$43.63	9.372%	$47.719	$47.72	$47.70	$47.70
Purchase #2	$91.34	8.683%	$99.2711	$99.27	$99.25	$99.30
Purchase #3	$67.91	12.704%	$76.5373	$76.54	$76.55	$76.50
Purchase #4	$90.35	11.209%	$100.4773	$100.48	$100.50	$100.50
Purchase #5	$34.78	12.151%	$39.0061	$39.01	$39.00	$39.00
Purchase #6	$83.54	9.782%	$91.7119	$91.71	$91.70	$91.70
Purchase #7	$45.46	11.246%	$50.5724	$50.57	$50.55	$50.60
7 purchase totals =	$457.01		$505.2951	$505.30	$505.25	$505.30