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	$93.69	11.223%	$104.2048	$104.20	$104.20	$104.20
Purchase #2	$37.52	12.721%	$42.2929	$42.29	$42.30	$42.30
Purchase #3	$125.74	4.334%	$131.1896	$131.19	$131.20	$131.20
Purchase #4	$99.90	4.427%	$104.3226	$104.32	$104.30	$104.30
Purchase #5	$187.43	8.252%	$202.8967	$202.90	$202.90	$202.90
Purchase #6	$237.33	12.757%	$267.6062	$267.61	$267.60	$267.60
Purchase #7	$91.33	9.152%	$99.6885	$99.69	$99.70	$99.70
7 purchase totals =	$872.94		$952.2013	$952.20	$952.20	$952.20