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	$39.90	13.630%	$45.3384	$45.34	$45.35	$45.30
Purchase #2	$166.86	4.844%	$174.9427	$174.94	$174.95	$174.90
Purchase #3	$150.49	4.736%	$157.6172	$157.62	$157.60	$157.60
Purchase #4	$38.90	11.596%	$43.4108	$43.41	$43.40	$43.40
Purchase #5	$211.25	8.683%	$229.5928	$229.59	$229.60	$229.60
Purchase #6	$17.30	6.247%	$18.3807	$18.38	$18.40	$18.40
Purchase #7	$224.89	9.407%	$246.0454	$246.05	$246.05	$246.00
7 purchase totals =	$849.59		$915.3280	$915.33	$915.35	$915.20