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	$53.49	9.408%	$58.5223	$58.52	$58.50	$58.50
Purchase #2	$56.84	9.675%	$62.3393	$62.34	$62.35	$62.30
Purchase #3	$168.66	6.828%	$180.1761	$180.18	$180.20	$180.20
Purchase #4	$116.63	12.587%	$131.3102	$131.31	$131.30	$131.30
Purchase #5	$99.44	3.600%	$103.0198	$103.02	$103.00	$103.00
Purchase #6	$143.81	4.491%	$150.2685	$150.27	$150.25	$150.30
Purchase #7	$169.47	9.201%	$185.0629	$185.06	$185.05	$185.10
7 purchase totals =	$808.34		$870.6991	$870.70	$870.65	$870.70