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	$69.37	3.638%	$71.8937	$71.89	$71.90	$71.90
Purchase #2	$141.59	6.606%	$150.9434	$150.94	$150.95	$150.90
Purchase #3	$94.93	9.756%	$104.1914	$104.19	$104.20	$104.20
Purchase #4	$243.61	4.822%	$255.3569	$255.36	$255.35	$255.40
Purchase #5	$96.61	13.460%	$109.6137	$109.61	$109.60	$109.60
Purchase #6	$199.91	9.154%	$218.2098	$218.21	$218.20	$218.20
Purchase #7	$220.54	4.697%	$230.8988	$230.90	$230.90	$230.90
7 purchase totals =	$1,066.56		$1,141.1077	$1,141.10	$1,141.10	$1,141.10