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	$126.37	4.249%	$131.7395	$131.74	$131.75	$131.70
Purchase #2	$150.38	11.838%	$168.182	$168.18	$168.20	$168.20
Purchase #3	$110.51	5.470%	$116.5549	$116.55	$116.55	$116.60
Purchase #4	$144.97	5.174%	$152.4707	$152.47	$152.45	$152.50
Purchase #5	$80.85	11.117%	$89.8381	$89.84	$89.85	$89.80
Purchase #6	$84.37	6.331%	$89.7115	$89.71	$89.70	$89.70
Purchase #7	$62.89	8.663%	$68.3382	$68.34	$68.35	$68.30
7 purchase totals =	$760.34		$816.8349	$816.83	$816.85	$816.80