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	$9.64	9.119%	$10.5191	$10.52	$10.50	$10.50
Purchase #2	$63.42	4.683%	$66.39	$66.39	$66.40	$66.40
Purchase #3	$80.89	5.375%	$85.2378	$85.24	$85.25	$85.20
Purchase #4	$135.33	7.207%	$145.0832	$145.08	$145.10	$145.10
Purchase #5	$31.90	11.402%	$35.5372	$35.54	$35.55	$35.50
Purchase #6	$85.96	9.131%	$93.809	$93.81	$93.80	$93.80
Purchase #7	$238.75	13.780%	$271.6498	$271.65	$271.65	$271.60
7 purchase totals =	$645.89		$708.2261	$708.23	$708.25	$708.10