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	$110.76	4.729%	$115.9978	$116.00	$116.00	$116.00
Purchase #2	$199.59	12.172%	$223.8841	$223.88	$223.90	$223.90
Purchase #3	$130.73	7.630%	$140.7047	$140.70	$140.70	$140.70
Purchase #4	$68.29	6.820%	$72.9474	$72.95	$72.95	$72.90
Purchase #5	$183.70	9.304%	$200.7914	$200.79	$200.80	$200.80
Purchase #6	$36.40	10.204%	$40.1143	$40.11	$40.10	$40.10
Purchase #7	$55.25	12.356%	$62.0767	$62.08	$62.10	$62.10
7 purchase totals =	$784.72		$856.5164	$856.51	$856.55	$856.50