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	$73.59	10.556%	$81.3582	$81.36	$81.35	$81.40
Purchase #2	$81.36	10.832%	$90.1729	$90.17	$90.15	$90.20
Purchase #3	$218.90	8.731%	$238.0122	$238.01	$238.00	$238.00
Purchase #4	$204.83	9.223%	$223.7215	$223.72	$223.70	$223.70
Purchase #5	$224.76	3.196%	$231.9433	$231.94	$231.95	$231.90
Purchase #6	$80.63	12.169%	$90.4419	$90.44	$90.45	$90.40
Purchase #7	$120.34	9.266%	$131.4907	$131.49	$131.50	$131.50
7 purchase totals =	$1,004.41		$1,087.1407	$1,087.13	$1,087.10	$1,087.10