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	$238.48	13.570%	$270.8417	$270.84	$270.85	$270.80
Purchase #2	$65.33	11.598%	$72.907	$72.91	$72.90	$72.90
Purchase #3	$226.66	6.438%	$241.2524	$241.25	$241.25	$241.30
Purchase #4	$97.34	12.500%	$109.5075	$109.51	$109.50	$109.50
Purchase #5	$185.60	13.252%	$210.1957	$210.20	$210.20	$210.20
Purchase #6	$33.73	13.372%	$38.2404	$38.24	$38.25	$38.20
Purchase #7	$42.71	11.475%	$47.611	$47.61	$47.60	$47.60
7 purchase totals =	$889.85		$990.5557	$990.56	$990.55	$990.50