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	$152.69	12.600%	$171.9289	$171.93	$171.95	$171.90
Purchase #2	$176.30	11.579%	$196.7138	$196.71	$196.70	$196.70
Purchase #3	$113.54	8.531%	$123.2261	$123.23	$123.25	$123.20
Purchase #4	$21.39	7.708%	$23.0387	$23.04	$23.05	$23.00
Purchase #5	$157.80	7.279%	$169.2863	$169.29	$169.30	$169.30
Purchase #6	$69.34	10.704%	$76.7622	$76.76	$76.75	$76.80
Purchase #7	$119.25	10.305%	$131.5387	$131.54	$131.55	$131.50
7 purchase totals =	$810.31		$892.4947	$892.50	$892.55	$892.40