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	$54.80	4.870%	$57.4688	$57.47	$57.45	$57.50
Purchase #2	$42.56	11.558%	$47.4791	$47.48	$47.50	$47.50
Purchase #3	$44.88	13.571%	$50.9707	$50.97	$50.95	$51.00
Purchase #4	$71.78	9.745%	$78.775	$78.78	$78.80	$78.80
Purchase #5	$85.65	4.464%	$89.4734	$89.47	$89.45	$89.50
Purchase #6	$171.42	10.112%	$188.754	$188.75	$188.75	$188.80
Purchase #7	$98.84	11.190%	$109.9002	$109.90	$109.90	$109.90
7 purchase totals =	$569.93		$622.8212	$622.82	$622.80	$623.00