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	$81.98	10.132%	$90.2862	$90.29	$90.30	$90.30
Purchase #2	$217.44	9.220%	$237.488	$237.49	$237.50	$237.50
Purchase #3	$64.40	4.767%	$67.4699	$67.47	$67.45	$67.50
Purchase #4	$128.29	10.697%	$142.0132	$142.01	$142.00	$142.00
Purchase #5	$183.80	3.438%	$190.119	$190.12	$190.10	$190.10
Purchase #6	$175.26	4.689%	$183.4779	$183.48	$183.50	$183.50
Purchase #7	$55.54	10.775%	$61.5244	$61.52	$61.50	$61.50
7 purchase totals =	$906.71		$972.3786	$972.38	$972.35	$972.40