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	$22.50	13.301%	$25.4927	$25.49	$25.50	$25.50
Purchase #2	$124.55	3.353%	$128.7262	$128.73	$128.75	$128.70
Purchase #3	$81.41	12.264%	$91.3941	$91.39	$91.40	$91.40
Purchase #4	$146.88	4.696%	$153.7775	$153.78	$153.80	$153.80
Purchase #5	$29.57	13.463%	$33.551	$33.55	$33.55	$33.60
Purchase #6	$172.53	7.148%	$184.8624	$184.86	$184.85	$184.90
Purchase #7	$190.90	9.456%	$208.9515	$208.95	$208.95	$209.00
7 purchase totals =	$768.34		$826.7554	$826.75	$826.80	$826.90