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	$91.64	8.270%	$99.2186	$99.22	$99.20	$99.20
Purchase #2	$199.96	4.335%	$208.6283	$208.63	$208.65	$208.60
Purchase #3	$116.92	12.849%	$131.9431	$131.94	$131.95	$131.90
Purchase #4	$169.77	6.430%	$180.6862	$180.69	$180.70	$180.70
Purchase #5	$35.36	8.651%	$38.419	$38.42	$38.40	$38.40
Purchase #6	$63.27	13.605%	$71.8779	$71.88	$71.90	$71.90
Purchase #7	$24.87	10.462%	$27.4719	$27.47	$27.45	$27.50
7 purchase totals =	$701.79		$758.2450	$758.25	$758.25	$758.20