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	$80.54	6.252%	$85.5754	$85.58	$85.60	$85.60
Purchase #2	$91.93	9.827%	$100.964	$100.96	$100.95	$101.00
Purchase #3	$111.96	6.365%	$119.0863	$119.09	$119.10	$119.10
Purchase #4	$90.49	3.727%	$93.8626	$93.86	$93.85	$93.90
Purchase #5	$65.45	12.801%	$73.8283	$73.83	$73.85	$73.80
Purchase #6	$6.53	10.179%	$7.1947	$7.19	$7.20	$7.20
Purchase #7	$126.84	10.812%	$140.5539	$140.55	$140.55	$140.60
7 purchase totals =	$573.74		$621.0652	$621.06	$621.10	$621.20