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	$227.66	10.118%	$250.6946	$250.69	$250.70	$250.70
Purchase #2	$221.64	10.744%	$245.453	$245.45	$245.45	$245.50
Purchase #3	$44.75	10.824%	$49.5937	$49.59	$49.60	$49.60
Purchase #4	$135.87	10.782%	$150.5195	$150.52	$150.50	$150.50
Purchase #5	$91.34	10.274%	$100.7243	$100.72	$100.70	$100.70
Purchase #6	$43.46	3.573%	$45.0128	$45.01	$45.00	$45.00
Purchase #7	$25.46	3.120%	$26.2544	$26.25	$26.25	$26.30
7 purchase totals =	$790.18		$868.2523	$868.23	$868.20	$868.30