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	$131.96	5.732%	$139.5239	$139.52	$139.50	$139.50
Purchase #2	$227.48	7.122%	$243.6811	$243.68	$243.70	$243.70
Purchase #3	$47.96	6.466%	$51.0611	$51.06	$51.05	$51.10
Purchase #4	$137.42	5.727%	$145.29	$145.29	$145.30	$145.30
Purchase #5	$149.42	4.790%	$156.5772	$156.58	$156.60	$156.60
Purchase #6	$75.73	10.405%	$83.6097	$83.61	$83.60	$83.60
Purchase #7	$172.89	7.295%	$185.5023	$185.50	$185.50	$185.50
7 purchase totals =	$942.86		$1,005.2453	$1,005.24	$1,005.25	$1,005.30