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	$33.84	11.653%	$37.7834	$37.78	$37.80	$37.80
Purchase #2	$168.47	11.549%	$187.9266	$187.93	$187.95	$187.90
Purchase #3	$147.78	7.715%	$159.1812	$159.18	$159.20	$159.20
Purchase #4	$62.52	9.718%	$68.5957	$68.60	$68.60	$68.60
Purchase #5	$170.96	4.574%	$178.7797	$178.78	$178.80	$178.80
Purchase #6	$120.43	13.300%	$136.4472	$136.45	$136.45	$136.40
Purchase #7	$123.54	11.271%	$137.4642	$137.46	$137.45	$137.50
7 purchase totals =	$827.54		$906.1780	$906.18	$906.25	$906.20