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	$39.65	8.155%	$42.8835	$42.88	$42.90	$42.90
Purchase #2	$246.37	9.769%	$270.4379	$270.44	$270.45	$270.40
Purchase #3	$229.97	6.722%	$245.4286	$245.43	$245.45	$245.40
Purchase #4	$196.94	13.423%	$223.3753	$223.38	$223.40	$223.40
Purchase #5	$224.62	13.649%	$255.2784	$255.28	$255.30	$255.30
Purchase #6	$213.35	3.833%	$221.5277	$221.53	$221.55	$221.50
Purchase #7	$124.86	3.116%	$128.7506	$128.75	$128.75	$128.80
7 purchase totals =	$1,275.76		$1,387.6820	$1,387.69	$1,387.80	$1,387.70