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	$183.37	13.465%	$208.0608	$208.06	$208.05	$208.10
Purchase #2	$67.53	8.105%	$73.0033	$73.00	$73.00	$73.00
Purchase #3	$38.27	9.431%	$41.8792	$41.88	$41.90	$41.90
Purchase #4	$68.37	5.519%	$72.1433	$72.14	$72.15	$72.10
Purchase #5	$49.90	10.322%	$55.0507	$55.05	$55.05	$55.10
Purchase #6	$125.99	9.187%	$137.5647	$137.56	$137.55	$137.60
Purchase #7	$56.35	7.333%	$60.4821	$60.48	$60.50	$60.50
7 purchase totals =	$589.78		$648.1841	$648.17	$648.20	$648.30