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	$127.46	12.423%	$143.2944	$143.29	$143.30	$143.30
Purchase #2	$83.36	8.225%	$90.2164	$90.22	$90.20	$90.20
Purchase #3	$121.95	10.135%	$134.3096	$134.31	$134.30	$134.30
Purchase #4	$73.32	12.265%	$82.3127	$82.31	$82.30	$82.30
Purchase #5	$81.78	10.871%	$90.6703	$90.67	$90.65	$90.70
Purchase #6	$200.65	11.379%	$223.482	$223.48	$223.50	$223.50
Purchase #7	$124.76	11.317%	$138.8791	$138.88	$138.90	$138.90
7 purchase totals =	$813.28		$903.1645	$903.16	$903.15	$903.20