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	$32.74	8.463%	$35.5108	$35.51	$35.50	$35.50
Purchase #2	$37.25	12.486%	$41.901	$41.90	$41.90	$41.90
Purchase #3	$249.92	10.350%	$275.7867	$275.79	$275.80	$275.80
Purchase #4	$21.30	12.159%	$23.8899	$23.89	$23.90	$23.90
Purchase #5	$139.39	11.449%	$155.3488	$155.35	$155.35	$155.30
Purchase #6	$170.47	9.451%	$186.5811	$186.58	$186.60	$186.60
Purchase #7	$80.96	12.234%	$90.8646	$90.86	$90.85	$90.90
7 purchase totals =	$732.03		$809.8829	$809.88	$809.90	$809.90