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	$89.30	12.124%	$100.1267	$100.13	$100.15	$100.10
Purchase #2	$39.48	9.798%	$43.3483	$43.35	$43.35	$43.30
Purchase #3	$246.85	11.196%	$274.4873	$274.49	$274.50	$274.50
Purchase #4	$137.85	12.272%	$154.767	$154.77	$154.75	$154.80
Purchase #5	$80.80	6.113%	$85.7393	$85.74	$85.75	$85.70
Purchase #6	$179.94	4.153%	$187.4129	$187.41	$187.40	$187.40
Purchase #7	$62.44	7.523%	$67.1374	$67.14	$67.15	$67.10
7 purchase totals =	$836.66		$913.0189	$913.03	$913.05	$912.90