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	$28.62	7.315%	$30.7136	$30.71	$30.70	$30.70
Purchase #2	$212.40	11.534%	$236.8982	$236.90	$236.90	$236.90
Purchase #3	$78.97	4.687%	$82.6713	$82.67	$82.65	$82.70
Purchase #4	$93.43	13.326%	$105.8805	$105.88	$105.90	$105.90
Purchase #5	$18.91	3.320%	$19.5378	$19.54	$19.55	$19.50
Purchase #6	$65.46	11.287%	$72.8485	$72.85	$72.85	$72.80
Purchase #7	$32.55	13.310%	$36.8824	$36.88	$36.90	$36.90
7 purchase totals =	$530.34		$585.4323	$585.43	$585.45	$585.40