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	$34.54	8.554%	$37.4946	$37.49	$37.50	$37.50
Purchase #2	$209.44	3.398%	$216.5568	$216.56	$216.55	$216.60
Purchase #3	$215.36	11.505%	$240.1372	$240.14	$240.15	$240.10
Purchase #4	$212.52	13.483%	$241.1741	$241.17	$241.15	$241.20
Purchase #5	$70.58	13.294%	$79.9629	$79.96	$79.95	$80.00
Purchase #6	$178.56	9.470%	$195.4696	$195.47	$195.45	$195.50
Purchase #7	$113.85	13.238%	$128.9215	$128.92	$128.90	$128.90
7 purchase totals =	$1,034.85		$1,139.7167	$1,139.71	$1,139.65	$1,139.80