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	$21.67	12.159%	$24.3049	$24.30	$24.30	$24.30
Purchase #2	$74.75	4.513%	$78.1235	$78.12	$78.10	$78.10
Purchase #3	$45.84	8.561%	$49.7644	$49.76	$49.75	$49.80
Purchase #4	$233.57	11.213%	$259.7602	$259.76	$259.75	$259.80
Purchase #5	$179.57	11.660%	$200.5079	$200.51	$200.50	$200.50
Purchase #6	$24.76	4.646%	$25.9103	$25.91	$25.90	$25.90
Purchase #7	$78.79	8.409%	$85.4155	$85.42	$85.40	$85.40
7 purchase totals =	$658.95		$723.7867	$723.78	$723.70	$723.80