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	$138.33	9.556%	$151.5488	$151.55	$151.55	$151.50
Purchase #2	$245.77	13.350%	$278.5803	$278.58	$278.60	$278.60
Purchase #3	$115.41	5.158%	$121.3628	$121.36	$121.35	$121.40
Purchase #4	$90.79	9.461%	$99.3796	$99.38	$99.40	$99.40
Purchase #5	$216.34	10.171%	$238.3439	$238.34	$238.35	$238.30
Purchase #6	$218.31	11.719%	$243.8937	$243.89	$243.90	$243.90
Purchase #7	$173.43	5.765%	$183.4282	$183.43	$183.45	$183.40
7 purchase totals =	$1,198.38		$1,316.5373	$1,316.53	$1,316.60	$1,316.50