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	$52.66	12.755%	$59.3768	$59.38	$59.40	$59.40
Purchase #2	$71.90	9.706%	$78.8786	$78.88	$78.90	$78.90
Purchase #3	$44.78	13.794%	$50.957	$50.96	$50.95	$51.00
Purchase #4	$213.29	4.589%	$223.0779	$223.08	$223.10	$223.10
Purchase #5	$37.77	9.506%	$41.3604	$41.36	$41.35	$41.40
Purchase #6	$108.35	4.219%	$112.9213	$112.92	$112.90	$112.90
Purchase #7	$34.44	6.393%	$36.6417	$36.64	$36.65	$36.60
7 purchase totals =	$563.19		$603.2137	$603.22	$603.25	$603.30