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	$80.64	3.788%	$83.6946	$83.69	$83.70	$83.70
Purchase #2	$122.40	4.686%	$128.1357	$128.14	$128.15	$128.10
Purchase #3	$42.43	8.197%	$45.908	$45.91	$45.90	$45.90
Purchase #4	$191.59	7.530%	$206.0167	$206.02	$206.00	$206.00
Purchase #5	$164.77	3.698%	$170.8632	$170.86	$170.85	$170.90
Purchase #6	$47.90	11.264%	$53.2955	$53.30	$53.30	$53.30
Purchase #7	$66.72	5.606%	$70.4603	$70.46	$70.45	$70.50
7 purchase totals =	$716.45		$758.3740	$758.38	$758.35	$758.40