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	$12.38	5.126%	$13.0146	$13.01	$13.00	$13.00
Purchase #2	$127.72	4.547%	$133.5274	$133.53	$133.55	$133.50
Purchase #3	$90.25	10.280%	$99.5277	$99.53	$99.55	$99.50
Purchase #4	$232.27	5.873%	$245.9112	$245.91	$245.90	$245.90
Purchase #5	$228.51	12.382%	$256.8041	$256.80	$256.80	$256.80
Purchase #6	$219.50	10.143%	$241.7639	$241.76	$241.75	$241.80
Purchase #7	$10.73	12.270%	$12.0466	$12.05	$12.05	$12.00
7 purchase totals =	$921.36		$1,002.5955	$1,002.59	$1,002.60	$1,002.50