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	$131.91	13.652%	$149.9184	$149.92	$149.90	$149.90
Purchase #2	$104.89	10.196%	$115.5846	$115.58	$115.60	$115.60
Purchase #3	$86.43	4.681%	$90.4758	$90.48	$90.50	$90.50
Purchase #4	$159.67	12.226%	$179.1913	$179.19	$179.20	$179.20
Purchase #5	$97.77	11.813%	$109.3196	$109.32	$109.30	$109.30
Purchase #6	$115.59	13.323%	$130.9901	$130.99	$131.00	$131.00
Purchase #7	$109.40	13.263%	$123.9097	$123.91	$123.90	$123.90
7 purchase totals =	$805.66		$899.3895	$899.39	$899.40	$899.40