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	$157.48	13.664%	$178.9981	$179.00	$179.00	$179.00
Purchase #2	$193.76	4.222%	$201.9405	$201.94	$201.95	$201.90
Purchase #3	$125.77	4.180%	$131.0272	$131.03	$131.05	$131.00
Purchase #4	$168.27	6.358%	$178.9686	$178.97	$178.95	$179.00
Purchase #5	$92.76	13.325%	$105.1203	$105.12	$105.10	$105.10
Purchase #6	$73.61	7.127%	$78.8562	$78.86	$78.85	$78.90
Purchase #7	$33.83	13.708%	$38.4674	$38.47	$38.45	$38.50
7 purchase totals =	$845.48		$913.3783	$913.39	$913.35	$913.40