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	$73.97	11.390%	$82.3952	$82.40	$82.40	$82.40
Purchase #2	$250.56	4.330%	$261.4092	$261.41	$261.40	$261.40
Purchase #3	$177.43	10.627%	$196.2855	$196.29	$196.30	$196.30
Purchase #4	$218.63	12.785%	$246.5818	$246.58	$246.60	$246.60
Purchase #5	$10.94	4.494%	$11.4316	$11.43	$11.45	$11.40
Purchase #6	$210.70	11.755%	$235.4678	$235.47	$235.45	$235.50
Purchase #7	$240.30	7.333%	$257.9212	$257.92	$257.90	$257.90
7 purchase totals =	$1,182.53		$1,291.4923	$1,291.50	$1,291.50	$1,291.50