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	$133.71	12.599%	$150.5561	$150.56	$150.55	$150.60
Purchase #2	$154.97	8.757%	$168.5407	$168.54	$168.55	$168.50
Purchase #3	$171.43	11.479%	$191.1084	$191.11	$191.10	$191.10
Purchase #4	$149.86	3.784%	$155.5307	$155.53	$155.55	$155.50
Purchase #5	$171.55	3.352%	$177.3004	$177.30	$177.30	$177.30
Purchase #6	$218.28	8.491%	$236.8142	$236.81	$236.80	$236.80
Purchase #7	$41.71	3.696%	$43.2516	$43.25	$43.25	$43.30
7 purchase totals =	$1,041.51		$1,123.1021	$1,123.10	$1,123.10	$1,123.10