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	$240.41	4.409%	$251.0097	$251.01	$251.00	$251.00
Purchase #2	$73.67	8.647%	$80.0402	$80.04	$80.05	$80.00
Purchase #3	$64.46	11.775%	$72.0502	$72.05	$72.05	$72.10
Purchase #4	$20.82	11.707%	$23.2574	$23.26	$23.25	$23.30
Purchase #5	$121.42	4.874%	$127.338	$127.34	$127.35	$127.30
Purchase #6	$53.53	11.230%	$59.5414	$59.54	$59.55	$59.50
Purchase #7	$73.93	3.490%	$76.5102	$76.51	$76.50	$76.50
7 purchase totals =	$648.24		$689.7471	$689.75	$689.75	$689.70