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	$29.95	12.744%	$33.7668	$33.77	$33.75	$33.80
Purchase #2	$199.77	11.600%	$222.9433	$222.94	$222.95	$222.90
Purchase #3	$137.62	13.187%	$155.7679	$155.77	$155.75	$155.80
Purchase #4	$35.96	13.596%	$40.8491	$40.85	$40.85	$40.80
Purchase #5	$19.85	10.269%	$21.8884	$21.89	$21.90	$21.90
Purchase #6	$87.57	12.673%	$98.6677	$98.67	$98.65	$98.70
Purchase #7	$47.68	8.684%	$51.8205	$51.82	$51.80	$51.80
7 purchase totals =	$558.40		$625.7037	$625.71	$625.65	$625.70