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	$31.92	11.394%	$35.557	$35.56	$35.55	$35.60
Purchase #2	$164.37	5.607%	$173.5862	$173.59	$173.60	$173.60
Purchase #3	$35.93	11.217%	$39.9603	$39.96	$39.95	$40.00
Purchase #4	$142.33	12.242%	$159.754	$159.75	$159.75	$159.80
Purchase #5	$112.95	6.781%	$120.6091	$120.61	$120.60	$120.60
Purchase #6	$190.83	3.213%	$196.9614	$196.96	$196.95	$197.00
Purchase #7	$212.32	13.471%	$240.9216	$240.92	$240.90	$240.90
7 purchase totals =	$890.65		$967.3496	$967.35	$967.30	$967.50