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	$223.91	10.852%	$248.2087	$248.21	$248.20	$248.20
Purchase #2	$53.36	4.423%	$55.7201	$55.72	$55.70	$55.70
Purchase #3	$25.79	6.378%	$27.4349	$27.43	$27.45	$27.40
Purchase #4	$84.56	8.835%	$92.0309	$92.03	$92.05	$92.00
Purchase #5	$85.27	4.525%	$89.1285	$89.13	$89.15	$89.10
Purchase #6	$195.27	10.473%	$215.7206	$215.72	$215.70	$215.70
Purchase #7	$42.50	7.661%	$45.7559	$45.76	$45.75	$45.80
7 purchase totals =	$710.66		$773.9996	$774.00	$774.00	$773.90