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	$64.72	12.831%	$73.0242	$73.02	$73.00	$73.00
Purchase #2	$67.36	7.271%	$72.2577	$72.26	$72.25	$72.30
Purchase #3	$102.82	9.710%	$112.8038	$112.80	$112.80	$112.80
Purchase #4	$107.47	13.408%	$121.8796	$121.88	$121.90	$121.90
Purchase #5	$179.46	11.740%	$200.5286	$200.53	$200.55	$200.50
Purchase #6	$18.60	12.148%	$20.8595	$20.86	$20.85	$20.90
Purchase #7	$61.42	11.338%	$68.3838	$68.38	$68.40	$68.40
7 purchase totals =	$601.85		$669.7372	$669.73	$669.75	$669.80