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	$42.71	10.175%	$47.0557	$47.06	$47.05	$47.10
Purchase #2	$82.48	8.779%	$89.7209	$89.72	$89.70	$89.70
Purchase #3	$243.86	8.317%	$264.1418	$264.14	$264.15	$264.10
Purchase #4	$85.48	12.192%	$95.9017	$95.90	$95.90	$95.90
Purchase #5	$150.99	12.641%	$170.0766	$170.08	$170.10	$170.10
Purchase #6	$115.43	6.219%	$122.6086	$122.61	$122.60	$122.60
Purchase #7	$29.34	13.568%	$33.3209	$33.32	$33.30	$33.30
7 purchase totals =	$750.29		$822.8262	$822.83	$822.80	$822.80