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	$145.50	6.757%	$155.3314	$155.33	$155.35	$155.30
Purchase #2	$231.61	3.778%	$240.3602	$240.36	$240.35	$240.40
Purchase #3	$148.66	12.591%	$167.3778	$167.38	$167.40	$167.40
Purchase #4	$194.38	4.628%	$203.3759	$203.38	$203.40	$203.40
Purchase #5	$18.89	11.323%	$21.0289	$21.03	$21.05	$21.00
Purchase #6	$181.36	4.119%	$188.8302	$188.83	$188.85	$188.80
Purchase #7	$82.62	3.493%	$85.5059	$85.51	$85.50	$85.50
7 purchase totals =	$1,003.02		$1,061.8103	$1,061.82	$1,061.90	$1,061.80