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	$141.69	6.410%	$150.7723	$150.77	$150.75	$150.80
Purchase #2	$248.83	9.201%	$271.7248	$271.72	$271.70	$271.70
Purchase #3	$82.57	9.280%	$90.2325	$90.23	$90.25	$90.20
Purchase #4	$118.59	6.566%	$126.3766	$126.38	$126.40	$126.40
Purchase #5	$84.47	9.526%	$92.5166	$92.52	$92.50	$92.50
Purchase #6	$128.44	9.154%	$140.1974	$140.20	$140.20	$140.20
Purchase #7	$124.62	10.340%	$137.5057	$137.51	$137.50	$137.50
7 purchase totals =	$929.21		$1,009.3259	$1,009.33	$1,009.30	$1,009.30