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	$208.84	12.764%	$235.4963	$235.50	$235.50	$235.50
Purchase #2	$10.42	3.790%	$10.8149	$10.81	$10.80	$10.80
Purchase #3	$74.34	5.471%	$78.4071	$78.41	$78.40	$78.40
Purchase #4	$108.98	9.712%	$119.5641	$119.56	$119.55	$119.60
Purchase #5	$185.57	12.742%	$209.2153	$209.22	$209.20	$209.20
Purchase #6	$110.51	11.623%	$123.3546	$123.35	$123.35	$123.40
Purchase #7	$73.90	11.500%	$82.3985	$82.40	$82.40	$82.40
7 purchase totals =	$772.56		$859.2508	$859.25	$859.20	$859.30