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	$91.43	12.573%	$102.9255	$102.93	$102.95	$102.90
Purchase #2	$154.70	12.840%	$174.5635	$174.56	$174.55	$174.60
Purchase #3	$32.48	7.411%	$34.8871	$34.89	$34.90	$34.90
Purchase #4	$38.98	11.483%	$43.4561	$43.46	$43.45	$43.50
Purchase #5	$148.58	6.588%	$158.3685	$158.37	$158.35	$158.40
Purchase #6	$247.56	10.467%	$273.4721	$273.47	$273.45	$273.50
Purchase #7	$137.51	3.750%	$142.6666	$142.67	$142.65	$142.70
7 purchase totals =	$851.24		$930.3394	$930.35	$930.30	$930.50