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	$26.29	9.648%	$28.8265	$28.83	$28.85	$28.80
Purchase #2	$232.69	7.798%	$250.8352	$250.84	$250.85	$250.80
Purchase #3	$50.96	10.502%	$56.3118	$56.31	$56.30	$56.30
Purchase #4	$39.89	10.783%	$44.1913	$44.19	$44.20	$44.20
Purchase #5	$189.97	3.598%	$196.8051	$196.81	$196.80	$196.80
Purchase #6	$226.34	6.572%	$241.2151	$241.22	$241.20	$241.20
Purchase #7	$250.54	12.321%	$281.409	$281.41	$281.40	$281.40
7 purchase totals =	$1,016.68		$1,099.5940	$1,099.61	$1,099.60	$1,099.50