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	$22.75	11.607%	$25.3906	$25.39	$25.40	$25.40
Purchase #2	$48.51	12.192%	$54.4243	$54.42	$54.40	$54.40
Purchase #3	$98.34	12.308%	$110.4437	$110.44	$110.45	$110.40
Purchase #4	$75.87	6.155%	$80.5398	$80.54	$80.55	$80.50
Purchase #5	$84.49	7.186%	$90.5615	$90.56	$90.55	$90.60
Purchase #6	$233.64	6.358%	$248.4948	$248.49	$248.50	$248.50
Purchase #7	$59.67	10.696%	$66.0523	$66.05	$66.05	$66.10
7 purchase totals =	$623.27		$675.9070	$675.89	$675.90	$675.90