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	$93.34	6.632%	$99.5303	$99.53	$99.55	$99.50
Purchase #2	$80.72	9.795%	$88.6265	$88.63	$88.65	$88.60
Purchase #3	$124.42	12.627%	$140.1305	$140.13	$140.15	$140.10
Purchase #4	$71.46	9.228%	$78.0543	$78.05	$78.05	$78.10
Purchase #5	$83.36	10.431%	$92.0553	$92.06	$92.05	$92.10
Purchase #6	$150.38	8.740%	$163.5232	$163.52	$163.50	$163.50
Purchase #7	$113.81	7.628%	$122.4914	$122.49	$122.50	$122.50
7 purchase totals =	$717.49		$784.4115	$784.41	$784.45	$784.40