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	$77.74	5.639%	$82.1238	$82.12	$82.10	$82.10
Purchase #2	$97.47	11.540%	$108.718	$108.72	$108.70	$108.70
Purchase #3	$177.38	3.874%	$184.2517	$184.25	$184.25	$184.30
Purchase #4	$164.98	11.696%	$184.2761	$184.28	$184.30	$184.30
Purchase #5	$37.96	11.556%	$42.3467	$42.35	$42.35	$42.30
Purchase #6	$143.48	3.331%	$148.2593	$148.26	$148.25	$148.30
Purchase #7	$131.57	4.340%	$137.2801	$137.28	$137.30	$137.30
7 purchase totals =	$830.58		$887.2557	$887.26	$887.25	$887.30