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	$181.56	10.477%	$200.582	$200.58	$200.60	$200.60
Purchase #2	$230.79	6.374%	$245.5006	$245.50	$245.50	$245.50
Purchase #3	$83.97	5.470%	$88.5632	$88.56	$88.55	$88.60
Purchase #4	$98.49	5.860%	$104.2615	$104.26	$104.25	$104.30
Purchase #5	$84.36	6.680%	$89.9952	$90.00	$90.00	$90.00
Purchase #6	$39.51	7.695%	$42.5503	$42.55	$42.55	$42.60
Purchase #7	$192.34	7.565%	$206.8905	$206.89	$206.90	$206.90
7 purchase totals =	$911.02		$978.3433	$978.34	$978.35	$978.50