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	$131.78	4.227%	$137.3503	$137.35	$137.35	$137.40
Purchase #2	$187.66	11.151%	$208.586	$208.59	$208.60	$208.60
Purchase #3	$133.48	12.244%	$149.8233	$149.82	$149.80	$149.80
Purchase #4	$214.36	7.659%	$230.7778	$230.78	$230.80	$230.80
Purchase #5	$174.76	5.781%	$184.8629	$184.86	$184.85	$184.90
Purchase #6	$83.87	7.160%	$89.8751	$89.88	$89.90	$89.90
Purchase #7	$80.47	12.443%	$90.4829	$90.48	$90.50	$90.50
7 purchase totals =	$1,006.38		$1,091.7583	$1,091.76	$1,091.80	$1,091.90