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	$93.86	13.284%	$106.3284	$106.33	$106.35	$106.30
Purchase #2	$84.71	11.254%	$94.2433	$94.24	$94.25	$94.20
Purchase #3	$78.80	10.416%	$87.0078	$87.01	$87.00	$87.00
Purchase #4	$186.39	7.781%	$200.893	$200.89	$200.90	$200.90
Purchase #5	$113.39	4.494%	$118.4857	$118.49	$118.50	$118.50
Purchase #6	$147.74	13.401%	$167.5386	$167.54	$167.55	$167.50
Purchase #7	$101.51	7.494%	$109.1172	$109.12	$109.10	$109.10
7 purchase totals =	$806.40		$883.6140	$883.62	$883.65	$883.50