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	$29.98	10.272%	$33.0595	$33.06	$33.05	$33.10
Purchase #2	$230.39	7.275%	$247.1509	$247.15	$247.15	$247.20
Purchase #3	$225.50	13.492%	$255.9245	$255.92	$255.90	$255.90
Purchase #4	$123.55	10.702%	$136.7723	$136.77	$136.75	$136.80
Purchase #5	$189.42	13.794%	$215.5486	$215.55	$215.55	$215.50
Purchase #6	$240.85	13.571%	$273.5358	$273.54	$273.55	$273.50
Purchase #7	$73.67	3.411%	$76.1829	$76.18	$76.20	$76.20
7 purchase totals =	$1,113.36		$1,238.1745	$1,238.17	$1,238.15	$1,238.20