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	$134.76	7.828%	$145.309	$145.31	$145.30	$145.30
Purchase #2	$248.89	3.641%	$257.9521	$257.95	$257.95	$258.00
Purchase #3	$171.89	8.447%	$186.4095	$186.41	$186.40	$186.40
Purchase #4	$147.31	5.582%	$155.5328	$155.53	$155.55	$155.50
Purchase #5	$63.77	11.517%	$71.1144	$71.11	$71.10	$71.10
Purchase #6	$227.64	9.846%	$250.0534	$250.05	$250.05	$250.10
Purchase #7	$45.54	13.413%	$51.6483	$51.65	$51.65	$51.60
7 purchase totals =	$1,039.80		$1,118.0195	$1,118.01	$1,118.00	$1,118.00