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	$97.48	7.617%	$104.9051	$104.91	$104.90	$104.90
Purchase #2	$80.60	10.549%	$89.1025	$89.10	$89.10	$89.10
Purchase #3	$31.81	7.774%	$34.2829	$34.28	$34.30	$34.30
Purchase #4	$157.35	4.367%	$164.2215	$164.22	$164.20	$164.20
Purchase #5	$193.75	12.394%	$217.7634	$217.76	$217.75	$217.80
Purchase #6	$72.83	9.561%	$79.7933	$79.79	$79.80	$79.80
Purchase #7	$119.56	10.321%	$131.8998	$131.90	$131.90	$131.90
7 purchase totals =	$753.38		$821.9685	$821.96	$821.95	$822.00