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	$37.48	13.203%	$42.4285	$42.43	$42.45	$42.40
Purchase #2	$38.36	11.202%	$42.6571	$42.66	$42.65	$42.70
Purchase #3	$179.94	7.426%	$193.3023	$193.30	$193.30	$193.30
Purchase #4	$179.35	11.228%	$199.4874	$199.49	$199.50	$199.50
Purchase #5	$200.41	4.481%	$209.3904	$209.39	$209.40	$209.40
Purchase #6	$5.85	13.736%	$6.6536	$6.65	$6.65	$6.70
Purchase #7	$102.99	6.711%	$109.9017	$109.90	$109.90	$109.90
7 purchase totals =	$744.38		$803.8210	$803.82	$803.85	$803.90