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	$233.78	9.333%	$255.5987	$255.60	$255.60	$255.60
Purchase #2	$99.53	3.124%	$102.6393	$102.64	$102.65	$102.60
Purchase #3	$171.47	8.127%	$185.4054	$185.41	$185.40	$185.40
Purchase #4	$160.60	13.351%	$182.0417	$182.04	$182.05	$182.00
Purchase #5	$176.78	8.317%	$191.4828	$191.48	$191.50	$191.50
Purchase #6	$176.67	13.327%	$200.2148	$200.21	$200.20	$200.20
Purchase #7	$210.49	8.795%	$229.0026	$229.00	$229.00	$229.00
7 purchase totals =	$1,229.32		$1,346.3853	$1,346.38	$1,346.40	$1,346.30