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	$155.53	6.364%	$165.4279	$165.43	$165.45	$165.40
Purchase #2	$171.93	5.210%	$180.8876	$180.89	$180.90	$180.90
Purchase #3	$10.67	10.836%	$11.8262	$11.83	$11.85	$11.80
Purchase #4	$228.38	3.414%	$236.1769	$236.18	$236.20	$236.20
Purchase #5	$250.93	5.436%	$264.5706	$264.57	$264.55	$264.60
Purchase #6	$225.75	7.151%	$241.8934	$241.89	$241.90	$241.90
Purchase #7	$137.64	3.241%	$142.1009	$142.10	$142.10	$142.10
7 purchase totals =	$1,180.83		$1,242.8835	$1,242.89	$1,242.95	$1,242.90