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	$71.43	12.666%	$80.4773	$80.48	$80.50	$80.50
Purchase #2	$10.97	11.280%	$12.2074	$12.21	$12.20	$12.20
Purchase #3	$139.74	6.262%	$148.4905	$148.49	$148.50	$148.50
Purchase #4	$171.73	10.838%	$190.3421	$190.34	$190.35	$190.30
Purchase #5	$245.38	11.600%	$273.8441	$273.84	$273.85	$273.80
Purchase #6	$76.31	11.773%	$85.294	$85.29	$85.30	$85.30
Purchase #7	$244.71	8.348%	$265.1384	$265.14	$265.15	$265.10
7 purchase totals =	$960.27		$1,055.7938	$1,055.79	$1,055.85	$1,055.70