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	$125.68	11.306%	$139.8894	$139.89	$139.90	$139.90
Purchase #2	$206.53	3.291%	$213.3269	$213.33	$213.35	$213.30
Purchase #3	$166.53	11.449%	$185.596	$185.60	$185.60	$185.60
Purchase #4	$145.65	13.571%	$165.4162	$165.42	$165.40	$165.40
Purchase #5	$85.59	3.231%	$88.3554	$88.36	$88.35	$88.40
Purchase #6	$225.35	6.719%	$240.4913	$240.49	$240.50	$240.50
Purchase #7	$130.84	5.340%	$137.8269	$137.83	$137.85	$137.80
7 purchase totals =	$1,086.17		$1,170.9021	$1,170.92	$1,170.95	$1,170.90