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	$84.81	5.238%	$89.2523	$89.25	$89.25	$89.30
Purchase #2	$141.66	4.307%	$147.7613	$147.76	$147.75	$147.80
Purchase #3	$233.49	7.869%	$251.8633	$251.86	$251.85	$251.90
Purchase #4	$111.72	6.806%	$119.3237	$119.32	$119.30	$119.30
Purchase #5	$37.38	12.455%	$42.0357	$42.04	$42.05	$42.00
Purchase #6	$159.37	8.256%	$172.5276	$172.53	$172.55	$172.50
Purchase #7	$165.74	12.586%	$186.6	$186.60	$186.60	$186.60
7 purchase totals =	$934.17		$1,009.3639	$1,009.36	$1,009.35	$1,009.40