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	$52.78	8.273%	$57.1465	$57.15	$57.15	$57.10
Purchase #2	$55.74	7.422%	$59.877	$59.88	$59.90	$59.90
Purchase #3	$11.88	13.629%	$13.4991	$13.50	$13.50	$13.50
Purchase #4	$139.70	4.297%	$145.7029	$145.70	$145.70	$145.70
Purchase #5	$133.94	5.664%	$141.5264	$141.53	$141.55	$141.50
Purchase #6	$186.69	6.260%	$198.3768	$198.38	$198.40	$198.40
Purchase #7	$223.74	13.183%	$253.2356	$253.24	$253.25	$253.20
7 purchase totals =	$804.47		$869.3643	$869.38	$869.45	$869.30