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	$124.73	9.628%	$136.739	$136.74	$136.75	$136.70
Purchase #2	$103.34	11.217%	$114.9316	$114.93	$114.95	$114.90
Purchase #3	$68.32	11.123%	$75.9192	$75.92	$75.90	$75.90
Purchase #4	$150.59	9.747%	$165.268	$165.27	$165.25	$165.30
Purchase #5	$84.29	7.782%	$90.8494	$90.85	$90.85	$90.80
Purchase #6	$152.26	9.781%	$167.1526	$167.15	$167.15	$167.20
Purchase #7	$31.78	13.564%	$36.0906	$36.09	$36.10	$36.10
7 purchase totals =	$715.31		$786.9504	$786.95	$786.95	$786.90