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	$13.90	6.686%	$14.8294	$14.83	$14.85	$14.80
Purchase #2	$34.98	7.807%	$37.7109	$37.71	$37.70	$37.70
Purchase #3	$195.26	8.704%	$212.2554	$212.26	$212.25	$212.30
Purchase #4	$140.83	5.496%	$148.57	$148.57	$148.55	$148.60
Purchase #5	$19.69	3.233%	$20.3266	$20.33	$20.35	$20.30
Purchase #6	$86.93	3.389%	$89.8761	$89.88	$89.90	$89.90
Purchase #7	$164.76	13.361%	$186.7736	$186.77	$186.75	$186.80
7 purchase totals =	$656.35		$710.3420	$710.35	$710.35	$710.40