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	$112.73	9.487%	$123.4247	$123.42	$123.40	$123.40
Purchase #2	$16.83	6.705%	$17.9585	$17.96	$17.95	$18.00
Purchase #3	$147.72	6.544%	$157.3868	$157.39	$157.40	$157.40
Purchase #4	$223.68	11.855%	$250.1973	$250.20	$250.20	$250.20
Purchase #5	$39.66	7.192%	$42.5123	$42.51	$42.50	$42.50
Purchase #6	$26.50	4.618%	$27.7238	$27.72	$27.70	$27.70
Purchase #7	$231.41	10.511%	$255.7335	$255.73	$255.75	$255.70
7 purchase totals =	$798.53		$874.9369	$874.93	$874.90	$874.90