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	$121.58	9.524%	$133.1593	$133.16	$133.15	$133.20
Purchase #2	$35.38	6.125%	$37.547	$37.55	$37.55	$37.50
Purchase #3	$171.91	10.292%	$189.603	$189.60	$189.60	$189.60
Purchase #4	$233.56	11.462%	$260.3306	$260.33	$260.35	$260.30
Purchase #5	$55.59	6.688%	$59.3079	$59.31	$59.30	$59.30
Purchase #6	$165.80	4.664%	$173.5329	$173.53	$173.55	$173.50
Purchase #7	$250.45	10.807%	$277.5161	$277.52	$277.50	$277.50
7 purchase totals =	$1,034.27		$1,130.9968	$1,131.00	$1,131.00	$1,130.90