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	$102.34	3.381%	$105.8001	$105.80	$105.80	$105.80
Purchase #2	$131.91	4.648%	$138.0412	$138.04	$138.05	$138.00
Purchase #3	$134.52	11.539%	$150.0423	$150.04	$150.05	$150.00
Purchase #4	$50.47	7.739%	$54.3759	$54.38	$54.40	$54.40
Purchase #5	$105.44	13.639%	$119.821	$119.82	$119.80	$119.80
Purchase #6	$84.85	4.119%	$88.345	$88.35	$88.35	$88.30
Purchase #7	$246.93	4.841%	$258.8839	$258.88	$258.90	$258.90
7 purchase totals =	$856.46		$915.3094	$915.31	$915.35	$915.20