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	$63.40	11.165%	$70.4786	$70.48	$70.50	$70.50
Purchase #2	$171.35	4.833%	$179.6313	$179.63	$179.65	$179.60
Purchase #3	$138.52	6.153%	$147.0431	$147.04	$147.05	$147.00
Purchase #4	$139.67	9.156%	$152.4582	$152.46	$152.45	$152.50
Purchase #5	$31.60	12.432%	$35.5285	$35.53	$35.55	$35.50
Purchase #6	$142.89	5.714%	$151.0547	$151.05	$151.05	$151.10
Purchase #7	$238.61	10.505%	$263.676	$263.68	$263.70	$263.70
7 purchase totals =	$926.04		$999.8704	$999.87	$999.95	$999.90