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	$101.34	9.150%	$110.6126	$110.61	$110.60	$110.60
Purchase #2	$183.30	3.322%	$189.3892	$189.39	$189.40	$189.40
Purchase #3	$172.62	12.767%	$194.6584	$194.66	$194.65	$194.70
Purchase #4	$217.46	11.645%	$242.7832	$242.78	$242.80	$242.80
Purchase #5	$213.78	7.151%	$229.0674	$229.07	$229.05	$229.10
Purchase #6	$8.94	11.460%	$9.9645	$9.96	$9.95	$10.00
Purchase #7	$111.39	11.157%	$123.8178	$123.82	$123.80	$123.80
7 purchase totals =	$1,008.83		$1,100.2931	$1,100.29	$1,100.25	$1,100.40