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	$131.67	5.648%	$139.1067	$139.11	$139.10	$139.10
Purchase #2	$45.89	12.588%	$51.6666	$51.67	$51.65	$51.70
Purchase #3	$69.86	3.180%	$72.0815	$72.08	$72.10	$72.10
Purchase #4	$68.44	7.301%	$73.4368	$73.44	$73.45	$73.40
Purchase #5	$187.56	13.416%	$212.723	$212.72	$212.70	$212.70
Purchase #6	$78.41	5.256%	$82.5312	$82.53	$82.55	$82.50
Purchase #7	$53.92	4.800%	$56.5082	$56.51	$56.50	$56.50
7 purchase totals =	$635.75		$688.0540	$688.06	$688.05	$688.00