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	$80.30	12.764%	$90.5495	$90.55	$90.55	$90.50
Purchase #2	$152.89	7.168%	$163.8492	$163.85	$163.85	$163.80
Purchase #3	$29.53	6.768%	$31.5286	$31.53	$31.55	$31.50
Purchase #4	$6.83	13.328%	$7.7403	$7.74	$7.75	$7.70
Purchase #5	$152.64	10.651%	$168.8977	$168.90	$168.90	$168.90
Purchase #6	$218.86	8.352%	$237.1392	$237.14	$237.15	$237.10
Purchase #7	$242.67	8.851%	$264.1487	$264.15	$264.15	$264.10
7 purchase totals =	$883.72		$963.8532	$963.86	$963.90	$963.60