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	$28.70	13.468%	$32.5653	$32.57	$32.55	$32.60
Purchase #2	$213.25	6.654%	$227.4397	$227.44	$227.45	$227.40
Purchase #3	$52.63	9.608%	$57.6867	$57.69	$57.70	$57.70
Purchase #4	$228.93	9.613%	$250.937	$250.94	$250.95	$250.90
Purchase #5	$77.54	3.240%	$80.0523	$80.05	$80.05	$80.10
Purchase #6	$71.76	7.722%	$77.3013	$77.30	$77.30	$77.30
Purchase #7	$126.72	13.546%	$143.8855	$143.89	$143.90	$143.90
7 purchase totals =	$799.53		$869.8678	$869.88	$869.90	$869.90