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	$116.46	3.107%	$120.0784	$120.08	$120.10	$120.10
Purchase #2	$78.62	11.654%	$87.7824	$87.78	$87.80	$87.80
Purchase #3	$151.78	8.698%	$164.9818	$164.98	$165.00	$165.00
Purchase #4	$204.92	9.255%	$223.8853	$223.89	$223.90	$223.90
Purchase #5	$168.71	10.551%	$186.5106	$186.51	$186.50	$186.50
Purchase #6	$159.94	3.836%	$166.0753	$166.08	$166.10	$166.10
Purchase #7	$222.72	3.824%	$231.2368	$231.24	$231.25	$231.20
7 purchase totals =	$1,103.15		$1,180.5506	$1,180.56	$1,180.65	$1,180.60