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	$24.85	10.655%	$27.4978	$27.50	$27.50	$27.50
Purchase #2	$50.33	9.333%	$55.0273	$55.03	$55.05	$55.00
Purchase #3	$84.85	13.614%	$96.4015	$96.40	$96.40	$96.40
Purchase #4	$67.46	3.338%	$69.7118	$69.71	$69.70	$69.70
Purchase #5	$117.59	11.768%	$131.428	$131.43	$131.45	$131.40
Purchase #6	$22.63	8.473%	$24.5474	$24.55	$24.55	$24.50
Purchase #7	$229.85	12.802%	$259.2754	$259.28	$259.30	$259.30
7 purchase totals =	$597.56		$663.8892	$663.90	$663.95	$663.80