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	$152.34	12.763%	$171.7832	$171.78	$171.80	$171.80
Purchase #2	$213.57	12.789%	$240.8835	$240.88	$240.90	$240.90
Purchase #3	$80.46	6.833%	$85.9578	$85.96	$85.95	$86.00
Purchase #4	$81.95	4.413%	$85.5665	$85.57	$85.55	$85.60
Purchase #5	$82.92	8.738%	$90.1655	$90.17	$90.15	$90.20
Purchase #6	$143.50	3.650%	$148.7378	$148.74	$148.75	$148.70
Purchase #7	$101.95	7.449%	$109.5443	$109.54	$109.55	$109.50
7 purchase totals =	$856.69		$932.6386	$932.64	$932.65	$932.70