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	$9.27	13.274%	$10.5005	$10.50	$10.50	$10.50
Purchase #2	$130.82	5.414%	$137.9026	$137.90	$137.90	$137.90
Purchase #3	$211.63	9.397%	$231.5169	$231.52	$231.50	$231.50
Purchase #4	$215.87	12.676%	$243.2337	$243.23	$243.25	$243.20
Purchase #5	$164.36	9.780%	$180.4344	$180.43	$180.45	$180.40
Purchase #6	$109.96	9.187%	$120.062	$120.06	$120.05	$120.10
Purchase #7	$162.42	6.290%	$172.6362	$172.64	$172.65	$172.60
7 purchase totals =	$1,004.33		$1,096.2863	$1,096.28	$1,096.30	$1,096.20