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	$40.70	4.181%	$42.4017	$42.40	$42.40	$42.40
Purchase #2	$194.44	7.519%	$209.0599	$209.06	$209.05	$209.10
Purchase #3	$210.47	10.489%	$232.5462	$232.55	$232.55	$232.50
Purchase #4	$98.67	3.451%	$102.0751	$102.08	$102.10	$102.10
Purchase #5	$149.81	12.390%	$168.3715	$168.37	$168.35	$168.40
Purchase #6	$86.39	9.419%	$94.5271	$94.53	$94.55	$94.50
Purchase #7	$154.63	8.301%	$167.4658	$167.47	$167.45	$167.50
7 purchase totals =	$935.11		$1,016.4473	$1,016.46	$1,016.45	$1,016.50